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diff --git a/Documentation/powerpc/ppc_htab.txt b/Documentation/powerpc/ppc_htab.txt new file mode 100644 index 00000000000..8b8c7df29fa --- /dev/null +++ b/Documentation/powerpc/ppc_htab.txt @@ -0,0 +1,118 @@ + Information about /proc/ppc_htab +===================================================================== + +This document and the related code was written by me (Cort Dougan), please +email me (cort@fsmlabs.com) if you have questions, comments or corrections. + +Last Change: 2.16.98 + +This entry in the proc directory is readable by all users but only +writable by root. + +The ppc_htab interface is a user level way of accessing the +performance monitoring registers as well as providing information +about the PTE hash table. + +1. Reading + + Reading this file will give you information about the memory management + hash table that serves as an extended tlb for page translation on the + powerpc. It will also give you information about performance measurement + specific to the cpu that you are using. + + Explanation of the 604 Performance Monitoring Fields: + MMCR0 - the current value of the MMCR0 register + PMC1 + PMC2 - the value of the performance counters and a + description of what events they are counting + which are based on MMCR0 bit settings. + Explanation of the PTE Hash Table fields: + + Size - hash table size in Kb. + Buckets - number of buckets in the table. + Address - the virtual kernel address of the hash table base. + Entries - the number of ptes that can be stored in the hash table. + User/Kernel - how many pte's are in use by the kernel or user at that time. + Overflows - How many of the entries are in their secondary hash location. + Percent full - ratio of free pte entries to in use entries. + Reloads - Count of how many hash table misses have occurred + that were fixed with a reload from the linux tables. + Should always be 0 on 603 based machines. + Non-error Misses - Count of how many hash table misses have occurred + that were completed with the creation of a pte in the linux + tables with a call to do_page_fault(). + Error Misses - Number of misses due to errors such as bad address + and permission violations. This includes kernel access of + bad user addresses that are fixed up by the trap handler. + + Note that calculation of the data displayed from /proc/ppc_htab takes + a long time and spends a great deal of time in the kernel. It would + be quite hard on performance to read this file constantly. In time + there may be a counter in the kernel that allows successive reads from + this file only after a given amount of time has passed to reduce the + possibility of a user slowing the system by reading this file. + +2. Writing + + Writing to the ppc_htab allows you to change the characteristics of + the powerpc PTE hash table and setup performance monitoring. + + Resizing the PTE hash table is not enabled right now due to many + complications with moving the hash table, rehashing the entries + and many many SMP issues that would have to be dealt with. + + Write options to ppc_htab: + + - To set the size of the hash table to 64Kb: + + echo 'size 64' > /proc/ppc_htab + + The size must be a multiple of 64 and must be greater than or equal to + 64. + + - To turn off performance monitoring: + + echo 'off' > /proc/ppc_htab + + - To reset the counters without changing what they're counting: + + echo 'reset' > /proc/ppc_htab + + Note that counting will continue after the reset if it is enabled. + + - To count only events in user mode or only in kernel mode: + + echo 'user' > /proc/ppc_htab + ...or... + echo 'kernel' > /proc/ppc_htab + + Note that these two options are exclusive of one another and the + lack of either of these options counts user and kernel. + Using 'reset' and 'off' reset these flags. + + - The 604 has 2 performance counters which can each count events from + a specific set of events. These sets are disjoint so it is not + possible to count _any_ combination of 2 events. One event can + be counted by PMC1 and one by PMC2. + + To start counting a particular event use: + + echo 'event' > /proc/ppc_htab + + and choose from these events: + + PMC1 + ---- + 'ic miss' - instruction cache misses + 'dtlb' - data tlb misses (not hash table misses) + + PMC2 + ---- + 'dc miss' - data cache misses + 'itlb' - instruction tlb misses (not hash table misses) + 'load miss time' - cycles to complete a load miss + +3. Bugs + + The PMC1 and PMC2 counters can overflow and give no indication of that + in /proc/ppc_htab. |