mirror of
https://github.com/torvalds/linux.git
synced 2024-11-15 16:41:58 +00:00
1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
119 lines
4.4 KiB
Plaintext
119 lines
4.4 KiB
Plaintext
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.
|