diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/device-drivers.tmpl | 1 | ||||
| -rw-r--r-- | Documentation/DocBook/kernel-api.tmpl | 1 | ||||
| -rw-r--r-- | Documentation/DocBook/kernel-locking.tmpl | 6 | ||||
| -rw-r--r-- | Documentation/block/cfq-iosched.txt | 45 | ||||
| -rw-r--r-- | Documentation/cgroups/blkio-controller.txt | 28 | ||||
| -rw-r--r-- | Documentation/gpio.txt | 22 | ||||
| -rw-r--r-- | Documentation/hwmon/sysfs-interface | 7 | ||||
| -rw-r--r-- | Documentation/kernel-doc-nano-HOWTO.txt | 5 | ||||
| -rw-r--r-- | Documentation/mutex-design.txt | 3 | ||||
| -rw-r--r-- | Documentation/networking/e1000.txt | 373 | ||||
| -rw-r--r-- | Documentation/networking/e1000e.txt | 302 | ||||
| -rw-r--r--[-rwxr-xr-x] | Documentation/networking/ixgbevf.txt | 40 | ||||
| -rw-r--r-- | Documentation/power/regulator/overview.txt | 2 | ||||
| -rw-r--r-- | Documentation/sound/alsa/HD-Audio-Models.txt | 1 | ||||
| -rw-r--r-- | Documentation/workqueue.txt | 380 |
15 files changed, 886 insertions, 330 deletions
diff --git a/Documentation/DocBook/device-drivers.tmpl b/Documentation/DocBook/device-drivers.tmpl index ecd35e9d441..feca0758391 100644 --- a/Documentation/DocBook/device-drivers.tmpl +++ b/Documentation/DocBook/device-drivers.tmpl @@ -46,7 +46,6 @@ <sect1><title>Atomic and pointer manipulation</title> !Iarch/x86/include/asm/atomic.h -!Iarch/x86/include/asm/unaligned.h </sect1> <sect1><title>Delaying, scheduling, and timer routines</title> diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl index a20c6f6fffc..6899f471fb1 100644 --- a/Documentation/DocBook/kernel-api.tmpl +++ b/Documentation/DocBook/kernel-api.tmpl @@ -57,7 +57,6 @@ </para> <sect1><title>String Conversions</title> -!Ilib/vsprintf.c !Elib/vsprintf.c </sect1> <sect1><title>String Manipulation</title> diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 0b1a3f97f28..a0d479d1e1d 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -1961,6 +1961,12 @@ machines due to caching. </sect1> </chapter> + <chapter id="apiref"> + <title>Mutex API reference</title> +!Iinclude/linux/mutex.h +!Ekernel/mutex.c + </chapter> + <chapter id="references"> <title>Further reading</title> diff --git a/Documentation/block/cfq-iosched.txt b/Documentation/block/cfq-iosched.txt new file mode 100644 index 00000000000..e578feed6d8 --- /dev/null +++ b/Documentation/block/cfq-iosched.txt @@ -0,0 +1,45 @@ +CFQ ioscheduler tunables +======================== + +slice_idle +---------- +This specifies how long CFQ should idle for next request on certain cfq queues +(for sequential workloads) and service trees (for random workloads) before +queue is expired and CFQ selects next queue to dispatch from. + +By default slice_idle is a non-zero value. That means by default we idle on +queues/service trees. This can be very helpful on highly seeky media like +single spindle SATA/SAS disks where we can cut down on overall number of +seeks and see improved throughput. + +Setting slice_idle to 0 will remove all the idling on queues/service tree +level and one should see an overall improved throughput on faster storage +devices like multiple SATA/SAS disks in hardware RAID configuration. The down +side is that isolation provided from WRITES also goes down and notion of +IO priority becomes weaker. + +So depending on storage and workload, it might be useful to set slice_idle=0. +In general I think for SATA/SAS disks and software RAID of SATA/SAS disks +keeping slice_idle enabled should be useful. For any configurations where +there are multiple spindles behind single LUN (Host based hardware RAID +controller or for storage arrays), setting slice_idle=0 might end up in better +throughput and acceptable latencies. + +CFQ IOPS Mode for group scheduling +=================================== +Basic CFQ design is to provide priority based time slices. Higher priority +process gets bigger time slice and lower priority process gets smaller time +slice. Measuring time becomes harder if storage is fast and supports NCQ and +it would be better to dispatch multiple requests from multiple cfq queues in +request queue at a time. In such scenario, it is not possible to measure time +consumed by single queue accurately. + +What is possible though is to measure number of requests dispatched from a +single queue and also allow dispatch from multiple cfq queue at the same time. +This effectively becomes the fairness in terms of IOPS (IO operations per +second). + +If one sets slice_idle=0 and if storage supports NCQ, CFQ internally switches +to IOPS mode and starts providing fairness in terms of number of requests +dispatched. Note that this mode switching takes effect only for group +scheduling. For non-cgroup users nothing should change. diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt index 48e0b21b005..6919d62591d 100644 --- a/Documentation/cgroups/blkio-controller.txt +++ b/Documentation/cgroups/blkio-controller.txt @@ -217,6 +217,7 @@ Details of cgroup files CFQ sysfs tunable ================= /sys/block/<disk>/queue/iosched/group_isolation +----------------------------------------------- If group_isolation=1, it provides stronger isolation between groups at the expense of throughput. By default group_isolation is 0. In general that @@ -243,6 +244,33 @@ By default one should run with group_isolation=0. If that is not sufficient and one wants stronger isolation between groups, then set group_isolation=1 but this will come at cost of reduced throughput. +/sys/block/<disk>/queue/iosched/slice_idle +------------------------------------------ +On a faster hardware CFQ can be slow, especially with sequential workload. +This happens because CFQ idles on a single queue and single queue might not +drive deeper request queue depths to keep the storage busy. In such scenarios +one can try setting slice_idle=0 and that would switch CFQ to IOPS +(IO operations per second) mode on NCQ supporting hardware. + +That means CFQ will not idle between cfq queues of a cfq group and hence be +able to driver higher queue depth and achieve better throughput. That also +means that cfq provides fairness among groups in terms of IOPS and not in +terms of disk time. + +/sys/block/<disk>/queue/iosched/group_idle +------------------------------------------ +If one disables idling on individual cfq queues and cfq service trees by +setting slice_idle=0, group_idle kicks in. That means CFQ will still idle +on the group in an attempt to provide fairness among groups. + +By default group_idle is same as slice_idle and does not do anything if +slice_idle is enabled. + +One can experience an overall throughput drop if you have created multiple +groups and put applications in that group which are not driving enough +IO to keep disk busy. In that case set group_idle=0, and CFQ will not idle +on individual groups and throughput should improve. + What works ========== - Currently only sync IO queues are support. All the buffered writes are diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index d96a6dba574..9633da01ff4 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -109,17 +109,19 @@ use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders. If you want to initialize a structure with an invalid GPIO number, use some negative number (perhaps "-EINVAL"); that will never be valid. To -test if a number could reference a GPIO, you may use this predicate: +test if such number from such a structure could reference a GPIO, you +may use this predicate: int gpio_is_valid(int number); A number that's not valid will be rejected by calls which may request or free GPIOs (see below). Other numbers may also be rejected; for -example, a number might be valid but unused on a given board. - -Whether a platform supports multiple GPIO controllers is currently a -platform-specific implementation issue. +example, a number might be valid but temporarily unused on a given board. +Whether a platform supports multiple GPIO controllers is a platform-specific +implementation issue, as are whether that support can leave "holes" in the space +of GPIO numbers, and whether new controllers can be added at runtime. Such issues +can affect things including whether adjacent GPIO numbers are both valid. Using GPIOs ----------- @@ -480,12 +482,16 @@ To support this framework, a platform's Kconfig will "select" either ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep(). -They may also want to provide a custom value for ARCH_NR_GPIOS. -ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled +It may also provide a custom value for ARCH_NR_GPIOS, so that it better +reflects the number of GPIOs in actual use on that platform, without +wasting static table space. (It should count both built-in/SoC GPIOs and +also ones on GPIO expanders. + +ARCH_REQUIRE_GPIOLIB means that the gpiolib code will always get compiled into the kernel on that architecture. -ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user +ARCH_WANT_OPTIONAL_GPIOLIB means the gpiolib code defaults to off and the user can enable it and build it into the kernel optionally. If neither of these options are selected, the platform does not support diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface index ff45d1f837c..48ceabedf55 100644 --- a/Documentation/hwmon/sysfs-interface +++ b/Documentation/hwmon/sysfs-interface @@ -91,12 +91,11 @@ name The chip name. I2C devices get this attribute created automatically. RO -update_rate The rate at which the chip will update readings. +update_interval The interval at which the chip will update readings. Unit: millisecond RW - Some devices have a variable update rate. This attribute - can be used to change the update rate to the desired - frequency. + Some devices have a variable update rate or interval. + This attribute can be used to change it to the desired value. ************ diff --git a/Documentation/kernel-doc-nano-HOWTO.txt b/Documentation/kernel-doc-nano-HOWTO.txt index 27a52b35d55..3d8a97747f7 100644 --- a/Documentation/kernel-doc-nano-HOWTO.txt +++ b/Documentation/kernel-doc-nano-HOWTO.txt @@ -345,5 +345,10 @@ documentation, in <filename>, for the functions listed. section titled <section title> from <filename>. Spaces are allowed in <section title>; do not quote the <section title>. +!C<filename> is replaced by nothing, but makes the tools check that +all DOC: sections and documented functions, symbols, etc. are used. +This makes sense to use when you use !F/!P only and want to verify +that all documentation is included. + Tim. */ <twaugh@redhat.com> diff --git a/Documentation/mutex-design.txt b/Documentation/mutex-design.txt index c91ccc0720f..38c10fd7f41 100644 --- a/Documentation/mutex-design.txt +++ b/Documentation/mutex-design.txt @@ -9,7 +9,7 @@ firstly, there's nothing wrong with semaphores. But if the simpler mutex semantics are sufficient for your code, then there are a couple of advantages of mutexes: - - 'struct mutex' is smaller on most architectures: .e.g on x86, + - 'struct mutex' is smaller on most architectures: E.g. on x86, 'struct semaphore' is 20 bytes, 'struct mutex' is 16 bytes. A smaller structure size means less RAM footprint, and better CPU-cache utilization. @@ -136,3 +136,4 @@ the APIs of 'struct mutex' have been streamlined: void mutex_lock_nested(struct mutex *lock, unsigned int subclass); int mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass); + int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock); diff --git a/Documentation/networking/e1000.txt b/Documentation/networking/e1000.txt index 2df71861e57..d9271e74e48 100644 --- a/Documentation/networking/e1000.txt +++ b/Documentation/networking/e1000.txt @@ -1,82 +1,35 @@ Linux* Base Driver for the Intel(R) PRO/1000 Family of Adapters =============================================================== -September 26, 2006 - +Intel Gigabit Linux driver. +Copyright(c) 1999 - 2010 Intel Corporation. Contents ======== -- In This Release - Identifying Your Adapter -- Building and Installation - Command Line Parameters - Speed and Duplex Configuration - Additional Configurations -- Known Issues - Support - -In This Release -=============== - -This file describes the Linux* Base Driver for the Intel(R) PRO/1000 Family -of Adapters. This driver includes support for Itanium(R)2-based systems. - -For questions related to hardware requirements, refer to the documentation -supplied with your Intel PRO/1000 adapter. All hardware requirements listed -apply to use with Linux. - -The following features are now available in supported kernels: - - Native VLANs - - Channel Bonding (teaming) - - SNMP - -Channel Bonding documentation can be found in the Linux kernel source: -/Documentation/networking/bonding.txt - -The driver information previously displayed in the /proc filesystem is not -supported in this release. Alternatively, you can use ethtool (version 1.6 -or later), lspci, and ifconfig to obtain the same information. - -Instructions on updating ethtool can be found in the section "Additional -Configurations" later in this document. - -NOTE: The Intel(R) 82562v 10/100 Network Connection only provides 10/100 -support. - - Identifying Your Adapter ======================== For more information on how to identify your adapter, go to the Adapter & Driver ID Guide at: - http://support.intel.com/support/network/adapter/pro100/21397.htm + http://support.intel.com/support/go/network/adapter/idguide.htm For the latest Intel network drivers for Linux, refer to the following website. In the search field, enter your adapter name or type, or use the networking link on the left to search for your adapter: - http://downloadfinder.intel.com/scripts-df/support_intel.asp - + http://support.intel.com/support/go/network/adapter/home.htm Command Line Parameters ======================= -If the driver is built as a module, the following optional parameters -are used by entering them on the command line with the modprobe command -using this syntax: - - modprobe e1000 [<option>=<VAL1>,<VAL2>,...] - -For example, with two PRO/1000 PCI adapters, entering: - - modprobe e1000 TxDescriptors=80,128 - -loads the e1000 driver with 80 TX descriptors for the first adapter and -128 TX descriptors for the second adapter. - The default value for each parameter is generally the recommended setting, unless otherwise noted. @@ -89,10 +42,6 @@ NOTES: For more information about the AutoNeg, Duplex, and Speed parameters, see the application note at: http://www.intel.com/design/network/applnots/ap450.htm - A descriptor describes a data buffer and attributes related to - the data buffer. This information is accessed by the hardware. - - AutoNeg ------- (Supported only on adapters with copper connections) @@ -106,7 +55,6 @@ Duplex parameters must not be specified. NOTE: Refer to the Speed and Duplex section of this readme for more information on the AutoNeg parameter. - Duplex ------ (Supported only on adapters with copper connections) @@ -119,7 +67,6 @@ set to auto-negotiate, the board auto-detects the correct duplex. If the link partner is forced (either full or half), Duplex defaults to half- duplex. - FlowControl ----------- Valid Range: 0-3 (0=none, 1=Rx only, 2=Tx only, 3=Rx&Tx) @@ -128,16 +75,16 @@ Default Value: Reads flow control settings from the EEPROM This parameter controls the automatic generation(Tx) and response(Rx) to Ethernet PAUSE frames. - InterruptThrottleRate --------------------- (not supported on Intel(R) 82542, 82543 or 82544-based adapters) -Valid Range: 0,1,3,100-100000 (0=off, 1=dynamic, 3=dynamic conservative) +Valid Range: 0,1,3,4,100-100000 (0=off, 1=dynamic, 3=dynamic conservative, + 4=simplified balancing) Default Value: 3 The driver can limit the amount of interrupts per second that the adapter -will generate for incoming packets. It does this by writing a value to the -adapter that is based on the maximum amount of interrupts that the adapter +will generate for incoming packets. It does this by writing a value to the +adapter that is based on the maximum amount of interrupts that the adapter will generate per second. Setting InterruptThrottleRate to a value greater or equal to 100 @@ -146,37 +93,43 @@ per second, even if more packets have come in. This reduces interrupt load on the system and can lower CPU utilization under heavy load, but will increase latency as packets are not processed as quickly. -The default behaviour of the driver previously assumed a static -InterruptThrottleRate value of 8000, providing a good fallback value for -all traffic types,but lacking in small packet performance and latency. -The hardware can handle many more small packets per second however, and +The default behaviour of the driver previously assumed a static +InterruptThrottleRate value of 8000, providing a good fallback value for +all traffic types,but lacking in small packet performance and latency. +The hardware can handle many more small packets per second however, and for this reason an adaptive interrupt moderation algorithm was implemented. Since 7.3.x, the driver has two adaptive modes (setting 1 or 3) in which -it dynamically adjusts the InterruptThrottleRate value based on the traffic +it dynamically adjusts the InterruptThrottleRate value based on the traffic that it receives. After determining the type of incoming traffic in the last -timeframe, it will adjust the InterruptThrottleRate to an appropriate value +timeframe, it will adjust the InterruptThrottleRate to an appropriate value for that traffic. The algorithm classifies the incoming traffic every interval into -classes. Once the class is determined, the InterruptThrottleRate value is -adjusted to suit that traffic type the best. There are three classes defined: +classes. Once the class is determined, the InterruptThrottleRate value is +adjusted to suit that traffic type the best. There are three classes defined: "Bulk traffic", for large amounts of packets of normal size; "Low latency", for small amounts of traffic and/or a significant percentage of small -packets; and "Lowest latency", for almost completely small packets or +packets; and "Lowest latency", for almost completely small packets or minimal traffic. -In dynamic conservative mode, the InterruptThrottleRate value is set to 4000 -for traffic that falls in class "Bulk traffic". If traffic falls in the "Low -latency" or "Lowest latency" class, the InterruptThrottleRate is increased +In dynamic conservative mode, the InterruptThrottleRate value is set to 4000 +for traffic that falls in class "Bulk traffic". If traffic falls in the "Low +latency" or "Lowest latency" class, the InterruptThrottleRate is increased stepwise to 20000. This default mode is suitable for most applications. For situations where low latency is vital such as cluster or grid computing, the algorithm can reduce latency even more when InterruptThrottleRate is set to mode 1. In this mode, which operates -the same as mode 3, the InterruptThrottleRate will be increased stepwise to +the same as mode 3, the InterruptThrottleRate will be increased stepwise to 70000 for traffic in class "Lowest latency". +In simplified mode the interrupt rate is based on the ratio of Tx and +Rx traffic. If the bytes per second rate is approximately equal, the +interrupt rate will drop as low as 2000 interrupts per second. If the +traffic is mostly transmit or mostly receive, the interrupt rate could +be as high as 8000. + Setting InterruptThrottleRate to 0 turns off any interrupt moderation and may improve small packet latency, but is generally not suitable for bulk throughput traffic. @@ -212,8 +165,6 @@ NOTE: When e1000 is loaded with default settings and multiple adapters be platform-specific. If CPU utilization is not a concern, use RX_POLLING (NAPI) and default driver settings. - - RxDescriptors ------------- Valid Range: 80-256 for 82542 and 82543-based adapters @@ -225,15 +176,14 @@ by the driver. Increasing this value allows the driver to buffer more incoming packets, at the expense of increased system memory utilization. Each descriptor is 16 bytes. A receive buffer is also allocated for each -descriptor and can be either 2048, 4096, 8192, or 16384 bytes, depending +descriptor and can be either 2048, 4096, 8192, or 16384 bytes, depending on the MTU setting. The maximum MTU size is 16110. -NOTE: MTU designates the frame size. It only needs to be set for Jumbo - Frames. Depending on the available system resources, the request - for a higher number of receive descriptors may be denied. In this +NOTE: MTU designates the frame size. It only needs to be set for Jumbo + Frames. Depending on the available system resources, the request + for a higher number of receive descriptors may be denied. In this case, use a lower number. - RxIntDelay ---------- Valid Range: 0-65535 (0=off) @@ -254,7 +204,6 @@ CAUTION: When setting RxIntDelay to a value other than 0, adapters may restoring the network connection. To eliminate the potential for the hang ensure that RxIntDelay is set to 0. - RxAbsIntDelay ------------- (This parameter is supported only on 82540, 82545 and later adapters.) @@ -268,7 +217,6 @@ packet is received within the set amount of time. Proper tuning, along with RxIntDelay, may improve traffic throughput in specific network conditions. - Speed ----- (This parameter is supported only on adapters with copper connections.) @@ -280,7 +228,6 @@ Speed forces the line speed to the specified value in megabits per second partner is set to auto-negotiate, the board will auto-detect the correct speed. Duplex should also be set when Speed is set to either 10 or 100. - TxDescriptors ------------- Valid Range: 80-256 for 82542 and 82543-based adapters @@ -295,6 +242,36 @@ NOTE: Depending on the available system resources, the request for a higher number of transmit descriptors may be denied. In this case, use a lower number. +TxDescriptorStep +---------------- +Valid Range: 1 (use every Tx Descriptor) + 4 (use every 4th Tx Descriptor) + +Default Value: 1 (use every Tx Descriptor) + +On certain non-Intel architectures, it has been observed that intense TX +traffic bursts of short packets may result in an improper descriptor +writeback. If this occurs, the driver will report a "TX Timeout" and reset +the adapter, after which the transmit flow will restart, though data may +have stalled for as much as 10 seconds before it resumes. + +The improper writeback does not occur on the first descriptor in a system +memory cache-line, which is typically 32 bytes, or 4 descriptors long. + +Setting TxDescriptorStep to a value of 4 will ensure that all TX descriptors +are aligned to the start of a system memory cache line, and so this problem +will not occur. + +NOTES: Setting TxDescriptorStep to 4 effectively reduces the number of + TxDescriptors available for transmits to 1/4 of the normal allocation. + This has a possible negative performance impact, which may be + compensated for by allocating more descriptors using the TxDescriptors + module parameter. + + There are other conditions which may result in "TX Timeout", which will + not be resolved by the use of the TxDescriptorStep parameter. As the + issue addressed by this parameter has never been observed on Intel + Architecture platforms, it should not be used on Intel platforms. TxIntDelay ---------- @@ -307,7 +284,6 @@ efficiency if properly tuned for specific network traffic. If the system is reporting dropped transmits, this value may be set too high causing the driver to run out of available transmit descriptors. - TxAbsIntDelay ------------- (This parameter is supported only on 82540, 82545 and later adapters.) @@ -330,6 +306,35 @@ Default Value: 1 A value of '1' indicates that the driver should enable IP checksum offload for received packets (both UDP and TCP) to the adapter hardware. +Copybreak +--------- +Valid Range: 0-xxxxxxx (0=off) +Default Value: 256 +Usage: insmod e1000.ko copybreak=128 + +Driver copies all packets below or equaling this size to a fresh Rx +buffer before handing it up the stack. + +This parameter is different than other parameters, in that it is a +single (not 1,1,1 etc.) parameter applied to all driver instances and +it is also available during runtime at +/sys/module/e1000/parameters/copybreak + +SmartPowerDownEnable +-------------------- +Valid Range: 0-1 +Default Value: 0 (disabled) + +Allows PHY to turn off in lower power states. The user can turn off +this parameter in supported chipsets. + +KumeranLockLoss +--------------- +Valid Range: 0-1 +Default Value: 1 (enabled) + +This workaround skips resetting the PHY at shutdown for the initial +silicon releases of ICH8 systems. Speed and Duplex Configuration ============================== @@ -385,40 +390,9 @@ If the link partner is forced to a specific speed and duplex, then this parameter should not be used. Instead, use the Speed and Duplex parameters previously mentioned to force the adapter to the same speed and duplex. - Additional Configurations ========================= - Configuring the Driver on Different Distributions - ------------------------------------------------- - Configuring a network driver to load properly when the system is started - is distribution dependent. Typically, the configuration process involves - adding an alias line to /etc/modules.conf or /etc/modprobe.conf as well - as editing other system startup scripts and/or configuration files. Many - popular Linux distributions ship with tools to make these changes for you. - To learn the proper way to configure a network device for your system, - refer to your distribution documentation. If during this process you are - asked for the driver or module name, the name for the Linux Base Driver - for the Intel(R) PRO/1000 Family of Adapters is e1000. - - As an example, if you install the e1000 driver for two PRO/1000 adapters - (eth0 and eth1) and set the speed and duplex to 10full and 100half, add - the following to modules.conf or or modprobe.conf: - - alias eth0 e1000 - alias eth1 e1000 - options e1000 Speed=10,100 Duplex=2,1 - - Viewing Link Messages - --------------------- - Link messages will not be displayed to the console if the distribution is - restricting system messages. In order to see network driver link messages - on your console, set dmesg to eight by entering the following: - - dmesg -n 8 - - NOTE: This setting is not saved across reboots. - Jumbo Frames ------------ Jumbo Frames support is enabled by changing the MTU to a value larger than @@ -437,9 +411,11 @@ Additional Configurations setting in a different location. Notes: - - - To enable Jumbo Frames, increase the MTU size on the interface beyond - 1500. + Degradation in throughput performance may be observed in some Jumbo frames + environments. If this is observed, increasing the application's socket buffer + size and/or increasing the /proc/sys/net/ipv4/tcp_*mem entry values may help. + See the specific application manual and /usr/src/linux*/Documentation/ + networking/ip-sysctl.txt for more details. - The maximum MTU setting for Jumbo Frames is 16110. This value coincides with the maximum Jumbo Frames size of 16128. @@ -447,40 +423,11 @@ Additional Configurations - Using Jumbo Frames at 10 or 100 Mbps may result in poor performance or loss of link. - - Some Intel gigabit adapters that support Jumbo Frames have a frame size - limit of 9238 bytes, with a corresponding MTU size limit of 9216 bytes. - The adapters with this limitation are based on the Intel(R) 82571EB, - 82572EI, 82573L and 80003ES2LAN controller. These correspond to the - following product names: - Intel(R) PRO/1000 PT Server Adapter - Intel(R) PRO/1000 PT Desktop Adapter - Intel(R) PRO/1000 PT Network Connection - Intel(R) PRO/1000 PT Dual Port Server Adapter - Intel(R) PRO/1000 PT Dual Port Network Connection - Intel(R) PRO/1000 PF Server Adapter - Intel(R) PRO/1000 PF Network Connection - Intel(R) PRO/1000 PF Dual Port Server Adapter - Intel(R) PRO/1000 PB Server Connection - Intel(R) PRO/1000 PL Network Connection - Intel(R) PRO/1000 EB Network Connection with I/O Acceleration - Intel(R) PRO/1000 EB Backplane Connection with I/O Acceleration - Intel(R) PRO/1000 PT Quad Port Server Adapter - - Adapters based on the Intel(R) 82542 and 82573V/E controller do not support Jumbo Frames. These correspond to the following product names: Intel(R) PRO/1000 Gigabit Server Adapter Intel(R) PRO/1000 PM Network Connection - - The following adapters do not support Jumbo Frames: - Intel(R) 82562V 10/100 Network Connection - Intel(R) 82566DM Gigabit Network Connection - Intel(R) 82566DC Gigabit Network Connection - Intel(R) 82566MM Gigabit Network Connection - Intel(R) 82566MC Gigabit Network Connection - Intel(R) 82562GT 10/100 Network Connection - Intel(R) 82562G 10/100 Network Connection - - Ethtool ------- The driver utilizes the ethtool interface for driver configuration and @@ -490,142 +437,14 @@ Additional Configurations The latest release of ethtool can be found from http://sourceforge.net/projects/gkernel. - NOTE: Ethtool 1.6 only supports a limited set of ethtool options. Support - for a more complete ethtool feature set can be enabled by upgrading - ethtool to ethtool-1.8.1. - Enabling Wake on LAN* (WoL) --------------------------- - WoL is configured through the Ethtool* utility. Ethtool is included with - all versions of Red Hat after Red Hat 7.2. For other Linux distributions, - download and install Ethtool from the following website: - http://sourceforge.net/projects/gkernel. - - For instructions on enabling WoL with Ethtool, refer to the website listed - above. + WoL is configured through the Ethtool* utility. WoL will be enabled on the system during the next shut down or reboot. For this driver version, in order to enable WoL, the e1000 driver must be loaded when shutting down or rebooting the system. - Wake On LAN is only supported on port A for the following devices: - Intel(R) PRO/1000 PT Dual Port Network Connection - Intel(R) PRO/1000 PT Dual Port Server Connection - Intel(R) PRO/1000 PT Dual Port Server Adapter - Intel(R) PRO/1000 PF Dual Port Server Adapter - Intel(R) PRO/1000 PT Quad Port Server Adapter - - NAPI - ---- - NAPI (Rx polling mode) is enabled in the e1000 driver. - - See www.cyberus.ca/~hadi/usenix-paper.tgz for more information on NAPI. - - -Known Issues -============ - -Dropped Receive Packets on Half-duplex 10/100 Networks ------------------------------------------------------- -If you have an Intel PCI Express adapter running at 10mbps or 100mbps, half- -duplex, you may observe occasional dropped receive packets. There are no -workarounds for this problem in this network configuration. The network must -be updated to operate in full-duplex, and/or 1000mbps only. - -Jumbo Frames System Requirement -------------------------------- -Memory allocation failures have been observed on Linux systems with 64 MB -of RAM or less that are running Jumbo Frames. If you are using Jumbo -Frames, your system may require more than the advertised minimum -requirement of 64 MB of system memory. - -Performance Degradation with Jumbo Frames ------------------------------------------ -Degradation in throughput performance may be observed in some Jumbo frames -environments. If this is observed, increasing the application's socket -buffer size and/or increasing the /proc/sys/net/ipv4/tcp_*mem entry values -may help. See the specific application manual and -/usr/src/linux*/Documentation/ -networking/ip-sysctl.txt for more details. - -Jumbo Frames on Foundry BigIron 8000 switch -------------------------------------------- -There is a known issue using Jumbo frames when connected to a Foundry -BigIron 8000 switch. This is a 3rd party limitation. If you experience -loss of packets, lower the MTU size. - -Allocating Rx Buffers when Using Jumbo Frames ---------------------------------------------- -Allocating Rx buffers when using Jumbo Frames on 2.6.x kernels may fail if -the available memory is heavily fragmented. This issue may be seen with PCI-X -adapters or with packet split disabled. This can be reduced or eliminated -by changing the amount of available memory for receive buffer allocation, by -increasing /proc/sys/vm/min_free_kbytes. - -Multiple Interfaces on Same Ethernet Broadcast Network ------------------------------------------------------- -Due to the default ARP behavior on Linux, it is not possible to have -one system on two IP networks in the same Ethernet broadcast domain -(non-partitioned switch) behave as expected. All Ethernet interfaces -will respond to IP traffic for any IP address assigned to the system. -This results in unbalanced receive traffic. - -If you have multiple interfaces in a server, either turn on ARP -filtering by entering: - - echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter -(this only works if your kernel's version is higher than 2.4.5), - -NOTE: This setting is not saved across reboots. The configuration -change can be made permanent by adding the line: - net.ipv4.conf.all.arp_filter = 1 -to the file /etc/sysctl.conf - - or, - -install the interfaces in separate broadcast domains (either in -different switches or in a switch partitioned to VLANs). - -82541/82547 can't link or are slow to link with some link partners ------------------------------------------------------------------ -There is a known compatibility issue with 82541/82547 and some -low-end switches where the link will not be established, or will -be slow to establish. In particular, these switches are known to -be incompatible with 82541/82547: - - Planex FXG-08TE - I-O Data ETG-SH8 - -To workaround this issue, the driver can be compiled with an override -of the PHY's master/slave setting. Forcing master or forcing slave -mode will improve time-to-link. - - # make CFLAGS_EXTRA=-DE1000_MASTER_SLAVE=<n> - -Where <n> is: - - 0 = Hardware default - 1 = Master mode - 2 = Slave mode - 3 = Auto master/slave - -Disable rx flow control with ethtool ------------------------------------- -In order to disable receive flow control using ethtool, you must turn -off auto-negotiation on the same command line. - -For example: - - ethtool -A eth? autoneg off rx off - -Unplugging network cable while ethtool -p is running ----------------------------------------------------- -In kernel versions 2.5.50 and later (including 2.6 kernel), unplugging -the network cable while ethtool -p is running will cause the system to -become unresponsive to keyboard commands, except for control-alt-delete. -Restarting the system appears to be the only remedy. - - Support ======= diff --git a/Documentation/networking/e1000e.txt b/Documentation/networking/e1000e.txt new file mode 100644 index 00000000000..6aa048badf3 --- /dev/null +++ b/Documentation/networking/e1000e.txt @@ -0,0 +1,302 @@ +Linux* Driver for Intel(R) Network Connection +=============================================================== + +Intel Gigabit Linux driver. +Copyright(c) 1999 - 2010 Intel Corporation. + +Contents +======== + +- Identifying Your Adapter +- Command Line Parameters +- Additional Configurations +- Support + +Identifying Your Adapter +======================== + +The e1000e driver supports all PCI Express Intel(R) Gigabit Network +Connections, except those that are 82575, 82576 and 82580-based*. + +* NOTE: The Intel(R) PRO/1000 P Dual Port Server Adapter is supported by + the e1000 driver, not the e1000e driver due to the 82546 part being used + behind a PCI Express bridge. + +For more information on how to identify your adapter, go to the Adapter & +Driver ID Guide at: + + http://support.intel.com/support/go/network/adapter/idguide.htm + +For the latest Intel network drivers for Linux, refer to the following +website. In the search field, enter your adapter name or type, or use the +networking link on the left to search for your adapter: + + http://support.intel.com/support/go/network/adapter/home.htm + +Command Line Parameters +======================= + +The default value for each parameter is generally the recommended setting, +unless otherwise noted. + +NOTES: For more information about the InterruptThrottleRate, + RxIntDelay, TxIntDelay, RxAbsIntDelay, and TxAbsIntDelay + parameters, see the application note at: + http://www.intel.com/design/network/applnots/ap450.htm + +InterruptThrottleRate +--------------------- +Valid Range: 0,1,3,4,100-100000 (0=off, 1=dynamic, 3=dynamic conservative, + 4=simplified balancing) +Default Value: 3 + +The driver can limit the amount of interrupts per second that the adapter +will generate for incoming packets. It does this by writing a value to the +adapter that is based on the maximum amount of interrupts that the adapter +will generate per second. + +Setting InterruptThrottleRate to a value greater or equal to 100 +will program the adapter to send out a maximum of that many interrupts +per second, even if more packets have come in. This reduces interrupt +load on the system and can lower CPU utilization under heavy load, +but will increase latency as packets are not processed as quickly. + +The driver has two adaptive modes (setting 1 or 3) in which +it dynamically adjusts the InterruptThrottleRate value based on the traffic +that it receives. After determining the type of incoming traffic in the last +timeframe, it will adjust the InterruptThrottleRate to an appropriate value +for that traffic. + +The algorithm classifies the incoming traffic every interval into +classes. Once the class is determined, the InterruptThrottleRate value is +adjusted to suit that traffic type the best. There are three classes defined: +"Bulk traffic", for large amounts of packets of normal size; "Low latency", +for small amounts of traffic and/or a significant percentage of small +packets; and "Lowest latency", for almost completely small packets or +minimal traffic. + +In dynamic conservative mode, the InterruptThrottleRate value is set to 4000 +for traffic that falls in class "Bulk traffic". If traffic falls in the "Low +latency" or "Lowest latency" class, the InterruptThrottleRate is increased +stepwise to 20000. This default mode is suitable for most applications. + +For situations where low latency is vital such as cluster or +grid computing, the algorithm can reduce latency even more when +InterruptThrottleRate is set to mode 1. In this mode, which operates +the same as mode 3, the InterruptThrottleRate will be increased stepwise to +70000 for traffic in class "Lowest latency". + +In simplified mode the interrupt rate is based on the ratio of Tx and +Rx traffic. If the bytes per second rate is approximately equal the +interrupt rate will drop as low as 2000 interrupts per second. If the +traffic is mostly transmit or mostly receive, the interrupt rate could +be as high as 8000. + +Setting InterruptThrottleRate to 0 turns off any interrupt moderation +and may improve small packet latency, but is generally not suitable +for bulk throughput traffic. + +NOTE: InterruptThrottleRate takes precedence over the TxAbsIntDelay and + RxAbsIntDelay parameters. In other words, minimizing the receive + and/or transmit absolute delays does not force the controller to + generate more interrupts than what the Interrupt Throttle Rate + allows. + +NOTE: When e1000e is loaded with default settings and multiple adapters + are in use simultaneously, the CPU utilization may increase non- + linearly. In order to limit the CPU utilization without impacting + the overall throughput, we recommend that you load the driver as + follows: + + modprobe e1000e InterruptThrottleRate=3000,3000,3000 + + This sets the InterruptThrottleRate to 3000 interrupts/sec for + the first, second, and third instances of the driver. The range + of 2000 to 3000 interrupts per second works on a majority of + systems and is a good starting point, but the optimal value will + be platform-specific. If CPU utilization is not a concern, use + RX_POLLING (NAPI) and default driver settings. + +RxIntDelay +---------- +Valid Range: 0-65535 (0=off) +Default Value: 0 + +This value delays the generation of receive interrupts in units of 1.024 +microseconds. Receive interrupt reduction can improve CPU efficiency if +properly tuned for specific network traffic. Increasing this value adds +extra latency to frame reception and can end up decreasing the throughput +of TCP traffic. If the system is reporting dropped receives, this value +may be set too high, causing the driver to run out of available receive +descriptors. + +CAUTION: When setting RxIntDelay to a value other than 0, adapters may + hang (stop transmitting) under certain network conditions. If + this occurs a NETDEV WATCHDOG message is logged in the system + event log. In addition, the controller is automatically reset, + restoring the network connection. To eliminate the potential + for the hang ensure that RxIntDelay is set to 0. + +RxAbsIntDelay +------------- +Valid Range: 0-65535 (0=off) +Default Value: 8 + +This value, in units of 1.024 microseconds, limits the delay in which a +receive interrupt is generated. Useful only if RxIntDelay is non-zero, +this value ensures that an interrupt is generated after the initial +packet is received within the set amount of time. Proper tuning, +along with RxIntDelay, may improve traffic throughput in specific network +conditions. + +TxIntDelay +---------- +Valid Range: 0-65535 (0=off) +Default Value: 8 + +This value delays the generation of transmit interrupts in units of +1.024 microseconds. Transmit interrupt reduction can improve CPU +efficiency if properly tuned for specific network traffic. If the +system is reporting dropped transmits, this value may be set too high +causing the driver to run out of available transmit descriptors. + +TxAbsIntDelay +------------- +Valid Range: 0-65535 (0=off) +Default Value: 32 + +This value, in units of 1.024 microseconds, limits the delay in which a +transmit interrupt is generated. Useful only if TxIntDelay is non-zero, +this value ensures that an interrupt is generated after the initial +packet is sent on the wire within the set amount of time. Proper tuning, +along with TxIntDelay, may improve traffic throughput in specific +network conditions. + +Copybreak +--------- +Valid Range: 0-xxxxxxx (0=off) +Default Value: 256 + +Driver copies all packets below or equaling this size to a fresh Rx +buffer before handing it up the stack. + +This parameter is different than other parameters, in that it is a +single (not 1,1,1 etc.) parameter applied to all driver instances and +it is also available during runtime at +/sys/module/e1000e/parameters/copybreak + +SmartPowerDownEnable +-------------------- +Valid Range: 0-1 +Default Value: 0 (disabled) + +Allows PHY to turn off in lower power states. The user can set this parameter +in supported chipsets. + +KumeranLockLoss +--------------- +Valid Range: 0-1 +Default Value: 1 (enabled) + +This workaround skips resetting the PHY at shutdown for the initial +silicon releases of ICH8 systems. + +IntMode +------- +Valid Range: 0-2 (0=legacy, 1=MSI, 2=MSI-X) +Default Value: 2 + +Allows changing the interrupt mode at module load time, without requiring a +recompile. If the driver load fails to enable a specific interrupt mode, the +driver will try other interrupt modes, from least to most compatible. The +interrupt order is MSI-X, MSI, Legacy. If specifying MSI (IntMode=1) +interrupts, only MSI and Legacy will be attempted. + +CrcStripping +------------ +Valid Range: 0-1 +Default Value: 1 (enabled) + +Strip the CRC from received packets before sending up the network stack. If +you have a machine with a BMC enabled but cannot receive IPMI traffic after +loading or enabling the driver, try disabling this feature. + +WriteProtectNVM +--------------- +Valid Range: 0-1 +Default Value: 1 (enabled) + +Set the hardware to ignore all write/erase cycles to the GbE region in the +ICHx NVM (non-volatile memory). This feature can be disabled by the +WriteProtectNVM module parameter (enabled by default) only after a hardware +reset, but the machine must be power cycled before trying to enable writes. + +Note: the kernel boot option iomem=relaxed may need to be set if the kernel +config option CONFIG_STRICT_DEVMEM=y, if the root user wants to write the +NVM from user space via ethtool. + +Additional Configurations +========================= + + Jumbo Frames + ------------ + Jumbo Frames support is enabled by changing the MTU to a value larger than + the default of 1500. Use the ifconfig command to increase the MTU size. + For example: + + ifconfig eth<x> mtu 9000 up + + This setting is not saved across reboots. + + Notes: + + - The maximum MTU setting for Jumbo Frames is 9216. This value coincides + with the maximum Jumbo Frames size of 9234 bytes. + + - Using Jumbo Frames at 10 or 100 Mbps is not supported and may result in + poor performance or loss of link. + + - Some adapters limit Jumbo Frames sized packets to a maximum of + 4096 bytes and some adapters do not support Jumbo Frames. + + + Ethtool + ------- + The driver utilizes the ethtool interface for driver configuration and + diagnostics, as well as displaying statistical information. We + strongly recommend downloading the latest version of Ethtool at: + + http://sourceforge.net/projects/gkernel. + + Speed and Duplex + ---------------- + Speed and Duplex are configured through the Ethtool* utility. For + instructions, refer to the Ethtool man page. + + Enabling Wake on LAN* (WoL) + --------------------------- + WoL is configured through the Ethtool* utility. For instructions on + enabling WoL with Ethtool, refer to the Ethtool man page. + + WoL will be enabled on the system during the next shut down or reboot. + For this driver version, in order to enable WoL, the e1000e driver must be + loaded when shutting down or rebooting the system. + + In most cases Wake On LAN is only supported on port A for multiple port + adapters. To verify if a port supports Wake on LAN run ethtool eth<X>. + + +Support +======= + +For general information, go to the Intel support website at: + + www.intel.com/support/ + +or the Intel Wired Networking project hosted by Sourceforge at: + + http://sourceforge.net/projects/e1000 + +If an issue is identified with the released source code on the supported +kernel with a supported adapter, email the specific information related +to the issue to e1000-devel@lists.sf.net diff --git a/Documentation/networking/ixgbevf.txt b/Documentation/networking/ixgbevf.txt index 19015de6725..21dd5d15b6b 100755..100644 --- a/Documentation/networking/ixgbevf.txt +++ b/Documentation/networking/ixgbevf.txt @@ -1,19 +1,16 @@ Linux* Base Driver for Intel(R) Network Connection ================================================== -November 24, 2009 +Intel Gigabit Linux driver. +Copyright(c) 1999 - 2010 Intel Corporation. Contents ======== -- In This Release - Identifying Your Adapter - Known Issues/Troubleshooting - Support -In This Release -=============== - This file describes the ixgbevf Linux* Base Driver for Intel Network Connection. @@ -33,7 +30,7 @@ Identifying Your Adapter For more information on how to identify your adapter, go to the Adapter & Driver ID Guide at: - http://support.intel.com/support/network/sb/CS-008441.htm + http://support.intel.com/support/go/network/adapter/idguide.htm Known Issues/Troubleshooting ============================ @@ -57,34 +54,3 @@ or the Intel Wired Networking project hosted by Sourceforge at: If an issue is identified with the released source code on the supported kernel with a supported adapter, email the specific information related to the issue to e1000-devel@lists.sf.net - -License -======= - -Intel 10 Gigabit Linux driver. -Copyright(c) 1999 - 2009 Intel Corporation. - -This program is free software; you can redistribute it and/or modify it -under the terms and conditions of the GNU General Public License, -version 2, as published by the Free Software Foundation. - -This program is distributed in the hope it will be useful, but WITHOUT -ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or -FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for -more details. - -You should have received a copy of the GNU General Public License along with -this program; if not, write to the Free Software Foundation, Inc., -51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA. - -The full GNU General Public License is included in this distribution in -the file called "COPYING". - -Trademarks -========== - -Intel, Itanium, and Pentium are trademarks or registered trademarks of -Intel Corporation or its subsidiaries in the United States and other -countries. - -* Other names and brands may be claimed as the property of others. diff --git a/Documentation/power/regulator/overview.txt b/Documentation/power/regulator/overview.txt index 9363e056188..8ed17587a74 100644 --- a/Documentation/power/regulator/overview.txt +++ b/Documentation/power/regulator/overview.txt @@ -13,7 +13,7 @@ regulators (where voltage output is controllable) and current sinks (where current limit is controllable). (C) 2008 Wolfson Microelectronics PLC. -Author: Liam Girdwood <lg@opensource.wolfsonmicro.com> +Author: Liam Girdwood <lrg@slimlogic.co.uk> Nomenclature diff --git a/Documentation/sound/alsa/HD-Audio-Models.txt b/Documentation/sound/alsa/HD-Audio-Models.txt index ce46fa1e643..37c6aad5e59 100644 --- a/Documentation/sound/alsa/HD-Audio-Models.txt +++ b/Documentation/sound/alsa/HD-Audio-Models.txt @@ -296,6 +296,7 @@ Conexant 5051 Conexant 5066 ============= laptop Basic Laptop config (default) + hp-laptop HP laptops, e g G60 dell-laptop Dell laptops dell-vostro Dell Vostro olpc-xo-1_5 OLPC XO 1.5 diff --git a/Documentation/workqueue.txt b/Documentation/workqueue.txt new file mode 100644 index 00000000000..e4498a2872c --- /dev/null +++ b/Documentation/workqueue.txt @@ -0,0 +1,380 @@ + +Concurrency Managed Workqueue (cmwq) + +September, 2010 Tejun Heo <tj@kernel.org> + Florian Mickler <florian@mickler.org> + +CONTENTS + +1. Introduction +2. Why cmwq? +3. The Design +4. Application Programming Interface (API) +5. Example Execution Scenarios +6. Guidelines + + +1. Introduction + +There are many cases where an asynchronous process execution context +is needed and the workqueue (wq) API is the most commonly used +mechanism for such cases. + +When such an asynchronous execution context is needed, a work item +describing which function to execute is put on a queue. An +independent thread serves as the asynchronous execution context. The +queue is called workqueue and the thread is called worker. + +While there are work items on the workqueue the worker executes the +functions associated with the work items one after the other. When +there is no work item left on the workqueue the worker becomes idle. +When a new work item gets queued, the worker begins executing again. + + +2. Why cmwq? + +In the original wq implementation, a multi threaded (MT) wq had one +worker thread per CPU and a single threaded (ST) wq had one worker +thread system-wide. A single MT wq needed to keep around the same +number of workers as the number of CPUs. The kernel grew a lot of MT +wq users over the years and with the number of CPU cores continuously +rising, some systems saturated the default 32k PID space just booting +up. + +Although MT wq wasted a lot of resource, the level of concurrency +provided was unsatisfactory. The limitation was common to both ST and +MT wq albeit less severe on MT. Each wq maintained its own separate +worker pool. A MT wq could provide only one execution context per CPU +while a ST wq one for the whole system. Work items had to compete for +those very limited execution contexts leading to various problems +including proneness to deadlocks around the single execution context. + +The tension between the provided level of concurrency and resource +usage also forced its users to make unnecessary tradeoffs like libata +choosing to use ST wq for polling PIOs and accepting an unnecessary +limitation that no two polling PIOs can progress at the same time. As +MT wq don't provide much better concurrency, users which require +higher level of concurrency, like async or fscache, had to implement +their own thread pool. + +Concurrency Managed Workqueue (cmwq) is a reimplementation of wq with +focus on the following goals. + +* Maintain compatibility with the original workqueue API. + +* Use per-CPU unified worker pools shared by all wq to provide + flexible level of concurrency on demand without wasting a lot of + resource. + +* Automatically regulate worker pool and level of concurrency so that + the API users don't need to worry about such details. + + +3. The Design + +In order to ease the asynchronous execution of functions a new +abstraction, the work item, is introduced. + +A work item is a simple struct that holds a pointer to the function +that is to be executed asynchronously. Whenever a driver or subsystem +wants a function to be executed asynchronously it has to set up a work +item pointing to that function and queue that work item on a +workqueue. + +Special purpose threads, called worker threads, execute the functions +off of the queue, one after the other. If no work is queued, the +worker threads become idle. These worker threads are managed in so +called thread-pools. + +The cmwq design differentiates between the user-facing workqueues that +subsystems and drivers queue work items on and the backend mechanism +which manages thread-pool and processes the queued work items. + +The backend is called gcwq. There is one gcwq for each possible CPU +and one gcwq to serve work items queued on unbound workqueues. + +Subsystems and drivers can create and queue work items through special +workqueue API functions as they see fit. They can influence some +aspects of the way the work items are executed by setting flags on the +workqueue they are putting the work item on. These flags include +things like CPU locality, reentrancy, concurrency limits and more. To +get a detailed overview refer to the API description of +alloc_workqueue() below. + +When a work item is queued to a workqueue, the target gcwq is +determined according to the queue parameters and workqueue attributes +and appended on the shared worklist of the gcwq. For example, unless +specifically overridden, a work item of a bound workqueue will be +queued on the worklist of exactly that gcwq that is associated to the +CPU the issuer is running on. + +For any worker pool implementation, managing the concurrency level +(how many execution contexts are active) is an important issue. cmwq +tries to keep the concurrency at a minimal but sufficient level. +Minimal to save resources and sufficient in that the system is used at +its full capacity. + +Each gcwq bound to an actual CPU implements concurrency management by +hooking into the scheduler. The gcwq is notified whenever an active +worker wakes up or sleeps and keeps track of the number of the +currently runnable workers. Generally, work items are not expected to +hog a CPU and consume many cycles. That means maintaining just enough +concurrency to prevent work processing from stalling should be +optimal. As long as there are one or more runnable workers on the +CPU, the gcwq doesn't start execution of a new work, but, when the +last running worker goes to sleep, it immediately schedules a new +worker so that the CPU doesn't sit idle while there are pending work +items. This allows using a minimal number of workers without losing +execution bandwidth. + +Keeping idle workers around doesn't cost other than the memory space +for kthreads, so cmwq holds onto idle ones for a while before killing +them. + +For an unbound wq, the above concurrency management doesn't apply and +the gcwq for the pseudo unbound CPU tries to start executing all work +items as soon as possible. The responsibility of regulating +concurrency level is on the users. There is also a flag to mark a +bound wq to ignore the concurrency management. Please refer to the +API section for details. + +Forward progress guarantee relies on that workers can be created when +more execution contexts are necessary, which in turn is guaranteed +through the use of rescue workers. All work items which might be used +on code paths that handle memory reclaim are required to be queued on +wq's that have a rescue-worker reserved for execution under memory +pressure. Else it is possible that the thread-pool deadlocks waiting +for execution contexts to free up. + + +4. Application Programming Interface (API) + +alloc_workqueue() allocates a wq. The original create_*workqueue() +functions are deprecated and scheduled for removal. alloc_workqueue() +takes three arguments - @name, @flags and @max_active. @name is the +name of the wq and also used as the name of the rescuer thread if +there is one. + +A wq no longer manages execution resources but serves as a domain for +forward progress guarantee, flush and work item attributes. @flags +and @max_active control how work items are assigned execution +resources, scheduled and executed. + +@flags: + + WQ_NON_REENTRANT + + By default, a wq guarantees non-reentrance only on the same + CPU. A work item may not be executed concurrently on the same + CPU by multiple workers but is allowed to be executed + concurrently on multiple CPUs. This flag makes sure + non-reentrance is enforced across all CPUs. Work items queued + to a non-reentrant wq are guaranteed to be executed by at most + one worker system-wide at any given time. + + WQ_UNBOUND + + Work items queued to an unbound wq are served by a special + gcwq which hosts workers which are not bound to any specific + CPU. This makes the wq behave as a simple execution context + provider without concurrency management. The unbound gcwq + tries to start execution of work items as soon as possible. + Unbound wq sacrifices locality but is useful for the following + cases. + + * Wide fluctuation in the concurrency level requirement is + expected and using bound wq may end up creating large number + of mostly unused workers across different CPUs as the issuer + hops through different CPUs. + + * Long running CPU intensive workloads which can be better + managed by the system scheduler. + + WQ_FREEZEABLE + + A freezeable wq participates in the freeze phase of the system + suspend operations. Work items on the wq are drained and no + new work item starts execution until thawed. + + WQ_RESCUER + + All wq which might be used in the memory reclaim paths _MUST_ + have this flag set. This reserves one worker exclusively for + the execution of this wq under memory pressure. + + WQ_HIGHPRI + + Work items of a highpri wq are queued at the head of the + worklist of the target gcwq and start execution regardless of + the current concurrency level. In other words, highpri work + items will always start execution as soon as execution + resource is available. + + Ordering among highpri work items is preserved - a highpri + work item queued after another highpri work item will start + execution after the earlier highpri work item starts. + + Although highpri work items are not held back by other + runnable work items, they still contribute to the concurrency + level. Highpri work items in runnable state will prevent + non-highpri work items from starting execution. + + This flag is meaningless for unbound wq. + + WQ_CPU_INTENSIVE + + Work items of a CPU intensive wq do not contribute to the + concurrency level. In other words, runnable CPU intensive + work items will not prevent other work items from starting + execution. This is useful for bound work items which are + expected to hog CPU cycles so that their execution is + regulated by the system scheduler. + + Although CPU intensive work items don't contribute to the + concurrency level, start of their executions is still + regulated by the concurrency management and runnable + non-CPU-intensive work items can delay execution of CPU + intensive work items. + + This flag is meaningless for unbound wq. + + WQ_HIGHPRI | WQ_CPU_INTENSIVE + + This combination makes the wq avoid interaction with + concurrency management completely and behave as a simple + per-CPU execution context provider. Work items queued on a + highpri CPU-intensive wq start execution as soon as resources + are available and don't affect execution of other work items. + +@max_active: + +@max_active determines the maximum number of execution contexts per +CPU which can be assigned to the work items of a wq. For example, +with @max_active of 16, at most 16 work items of the wq can be +executing at the same time per CPU. + +Currently, for a bound wq, the maximum limit for @max_active is 512 +and the default value used when 0 is specified is 256. For an unbound +wq, the limit is higher of 512 and 4 * num_possible_cpus(). These +values are chosen sufficiently high such that they are not the +limiting factor while providing protection in runaway cases. + +The number of active work items of a wq is usually regulated by the +users of the wq, more specifically, by how many work items the users +may queue at the same time. Unless there is a specific need for +throttling the number of active work items, specifying '0' is +recommended. + +Some users depend on the strict execution ordering of ST wq. The +combination of @max_active of 1 and WQ_UNBOUND is used to achieve this +behavior. Work items on such wq are always queued to the unbound gcwq +and only one work item can be active at any given time thus achieving +the same ordering property as ST wq. + + +5. Example Execution Scenarios + +The following example execution scenarios try to illustrate how cmwq +behave under different configurations. + + Work items w0, w1, w2 are queued to a bound wq q0 on the same CPU. + w0 burns CPU for 5ms then sleeps for 10ms then burns CPU for 5ms + again before finishing. w1 and w2 burn CPU for 5ms then sleep for + 10ms. + +Ignoring all other tasks, works and processing overhead, and assuming +simple FIFO scheduling, the following is one highly simplified version +of possible sequences of events with the original wq. + + TIME IN MSECS EVENT + 0 w0 starts and burns CPU + 5 w0 sleeps + 15 w0 wakes up and burns CPU + 20 w0 finishes + 20 w1 starts and burns CPU + 25 w1 sleeps + 35 w1 wakes up and finishes + 35 w2 starts and burns CPU + 40 w2 sleeps + 50 w2 wakes up and finishes + +And with cmwq with @max_active >= 3, + + TIME IN MSECS EVENT + 0 w0 starts and burns CPU + 5 w0 sleeps + 5 w1 starts and burns CPU + 10 w1 sleeps + 10 w2 starts and burns CPU + 15 w2 sleeps + 15 w0 wakes up and burns CPU + 20 w0 finishes + 20 w1 wakes up and finishes + 25 w2 wakes up and finishes + +If @max_active == 2, + + TIME IN MSECS EVENT + 0 w0 starts and burns CPU + 5 w0 sleeps + 5 w1 starts and burns CPU + 10 w1 sleeps + 15 w0 wakes up and burns CPU + 20 w0 finishes + 20 w1 wakes up and finishes + 20 w2 starts and burns CPU + 25 w2 sleeps + 35 w2 wakes up and finishes + +Now, let's assume w1 and w2 are queued to a different wq q1 which has +WQ_HIGHPRI set, + + TIME IN MSECS EVENT + 0 w1 and w2 start and burn CPU + 5 w1 sleeps + 10 w2 sleeps + 10 w0 starts and burns CPU + 15 w0 sleeps + 15 w1 wakes up and finishes + 20 w2 wakes up and finishes + 25 w0 wakes up and burns CPU + 30 w0 finishes + +If q1 has WQ_CPU_INTENSIVE set, + + TIME IN MSECS EVENT + 0 w0 starts and burns CPU + 5 w0 sleeps + 5 w1 and w2 start and burn CPU + 10 w1 sleeps + 15 w2 sleeps + 15 w0 wakes up and burns CPU + 20 w0 finishes + 20 w1 wakes up and finishes + 25 w2 wakes up and finishes + + +6. Guidelines + +* Do not forget to use WQ_RESCUER if a wq may process work items which + are used during memory reclaim. Each wq with WQ_RESCUER set has one + rescuer thread reserved for it. If there is dependency among + multiple work items used during memory reclaim, they should be + queued to separate wq each with WQ_RESCUER. + +* Unless strict ordering is required, there is no need to use ST wq. + +* Unless there is a specific need, using 0 for @max_active is + recommended. In most use cases, concurrency level usually stays + well under the default limit. + +* A wq serves as a domain for forward progress guarantee (WQ_RESCUER), + flush and work item attributes. Work items which are not involved + in memory reclaim and don't need to be flushed as a part of a group + of work items, and don't require any special attribute, can use one + of the system wq. There is no difference in execution + characteristics between using a dedicated wq and a system wq. + +* Unless work items are expected to consume a huge amount of CPU + cycles, using a bound wq is usually beneficial due to the increased + level of locality in wq operations and work item execution. |