linux-kernel - Re: missing madvise functionality

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Date:	Thu, 05 Apr 2007 11:47:17 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

Andrew Morton wrote:
> On Thu, 05 Apr 2007 03:39:29 -0400 Rik van Riel <riel@...hat.com> wrote:
> 
>> Rik van Riel wrote:
>>
>>> MADV_DONTNEED, unpatched, 1000 loops
>>>
>>> real    0m13.672s
>>> user    0m1.217s
>>> sys     0m45.712s
>>>
>>>
>>> MADV_DONTNEED, with patch, 1000 loops
>>>
>>> real    0m4.169s
>>> user    0m2.033s
>>> sys     0m3.224s
>> I just noticed something fun with these numbers.
>>
>> Without the patch, the system (a quad core CPU) is 10% idle.
>>
>> With the patch, it is 66% idle - presumably I need Nick's
>> mmap_sem patch.
>>
>> However, despite being 66% idle, the test still runs over
>> 3 times as fast!
> 
> Please quote the context switch rate when testing this stuff (I use vmstat 1).
> I've seen it vary by a factor of 10,000 depending upon what's happening.

About context switches 14000 per second.

I'll go compile in Nick's patch to see if that makes
things go faster.  I expect it will.

procs -----------memory---------- ---swap-- -----io---- --system-- 
-----cpu------
  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy 
id wa st
  1  0      0 965232 250024 370848    0    0     0     0 1026 13914 13 
21 67  0  0
  1  0      0 965232 250024 370848    0    0     0     0 1018 14654 12 
20 68  0  0
  1  0      0 965232 250024 370848    0    0     0     0 1023 14006 12 
21 67  0  0


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