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Date: Thu, 7 Jan 2010 10:00:54 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Minchan Kim <minchan.kim@gmail.com>,
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Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
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On Wed, 6 Jan 2010 01:39:17 -0800 (PST)
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> 
> 
> On Wed, 6 Jan 2010, KAMEZAWA Hiroyuki wrote:
> >
> >      9.08%  multi-fault-all  [kernel]                  [k] down_read_trylock
<snip>
> That way, it will do the cmpxchg first, and if it wasn't unlocked and had 
> other readers active, it will end up doing an extra cmpxchg, but still 
> hopefully avoid the extra bus cycles.
> 
> So it might be worth testing this trivial patch on top of my other one.
> 
Test: on 8-core/2-socket x86-64
  while () {
	touch memory
	barrier
	madvice DONTNEED all range by cpu 0
	barrier
  }

<Before> (cut from my post)
> [root@bluextal memory]#  /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-all 8
> 
>  Performance counter stats for './multi-fault-all 8' (5 runs):
> 
>        33029186  page-faults                ( +-   0.146% )
>       348698659  cache-misses               ( +-   0.149% )
> 
>    60.002876268  seconds time elapsed   ( +-   0.001% )
>     41.51%  multi-fault-all  [kernel]                  [k] clear_page_c
>      9.08%  multi-fault-all  [kernel]                  [k] down_read_trylock
>      6.23%  multi-fault-all  [kernel]                  [k] up_read
>      6.17%  multi-fault-all  [kernel]                  [k] __mem_cgroup_try_charg


<After>
[root@bluextal memory]#  /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-all 8

 Performance counter stats for './multi-fault-all 8' (5 runs):

       33782787  page-faults                ( +-   2.650% )
      332753197  cache-misses               ( +-   0.477% )

   60.003984337  seconds time elapsed   ( +-   0.004% )

# Samples: 1014408915089
#
# Overhead          Command             Shared Object  Symbol
# ........  ...............  ........................  ......
#
    44.42%  multi-fault-all  [kernel]                  [k] clear_page_c
     7.73%  multi-fault-all  [kernel]                  [k] down_read_trylock
     6.65%  multi-fault-all  [kernel]                  [k] __mem_cgroup_try_char
     6.15%  multi-fault-all  [kernel]                  [k] up_read
     4.87%  multi-fault-all  [kernel]                  [k] handle_mm_fault
     3.70%  multi-fault-all  [kernel]                  [k] __rmqueue
     3.69%  multi-fault-all  [kernel]                  [k] __mem_cgroup_commit_c
     2.35%  multi-fault-all  [kernel]                  [k] bad_range


yes, it seems slightly improved, at least on this test.
but page-fault-throughput test score is within error range.


Thanks,
-Kame



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