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116 files changed, 1092 insertions, 1205 deletions
diff --git a/Documentation/block/00-INDEX b/Documentation/block/00-INDEX index 961a0513f8c..a406286f6f3 100644 --- a/Documentation/block/00-INDEX +++ b/Documentation/block/00-INDEX @@ -1,7 +1,5 @@ 00-INDEX - This file -as-iosched.txt - - Anticipatory IO scheduler barrier.txt - I/O Barriers biodoc.txt diff --git a/Documentation/block/as-iosched.txt b/Documentation/block/as-iosched.txt deleted file mode 100644 index 738b72be128..00000000000 --- a/Documentation/block/as-iosched.txt +++ /dev/null @@ -1,172 +0,0 @@ -Anticipatory IO scheduler -------------------------- -Nick Piggin <piggin@cyberone.com.au> 13 Sep 2003 - -Attention! Database servers, especially those using "TCQ" disks should -investigate performance with the 'deadline' IO scheduler. Any system with high -disk performance requirements should do so, in fact. - -If you see unusual performance characteristics of your disk systems, or you -see big performance regressions versus the deadline scheduler, please email -me. Database users don't bother unless you're willing to test a lot of patches -from me ;) its a known issue. - -Also, users with hardware RAID controllers, doing striping, may find -highly variable performance results with using the as-iosched. The -as-iosched anticipatory implementation is based on the notion that a disk -device has only one physical seeking head. A striped RAID controller -actually has a head for each physical device in the logical RAID device. - -However, setting the antic_expire (see tunable parameters below) produces -very similar behavior to the deadline IO scheduler. - -Selecting IO schedulers ------------------------ -Refer to Documentation/block/switching-sched.txt for information on -selecting an io scheduler on a per-device basis. - -Anticipatory IO scheduler Policies ----------------------------------- -The as-iosched implementation implements several layers of policies -to determine when an IO request is dispatched to the disk controller. -Here are the policies outlined, in order of application. - -1. one-way Elevator algorithm. - -The elevator algorithm is similar to that used in deadline scheduler, with -the addition that it allows limited backward movement of the elevator -(i.e. seeks backwards). A seek backwards can occur when choosing between -two IO requests where one is behind the elevator's current position, and -the other is in front of the elevator's position. If the seek distance to -the request in back of the elevator is less than half the seek distance to -the request in front of the elevator, then the request in back can be chosen. -Backward seeks are also limited to a maximum of MAXBACK (1024*1024) sectors. -This favors forward movement of the elevator, while allowing opportunistic -"short" backward seeks. - -2. FIFO expiration times for reads and for writes. - -This is again very similar to the deadline IO scheduler. The expiration -times for requests on these lists is tunable using the parameters read_expire -and write_expire discussed below. When a read or a write expires in this way, -the IO scheduler will interrupt its current elevator sweep or read anticipation -to service the expired request. - -3. Read and write request batching - -A batch is a collection of read requests or a collection of write -requests. The as scheduler alternates dispatching read and write batches -to the driver. In the |