linux-kernel - Re: [PATCH -v6 0/2] Fixing the issue with memory-mapped file times

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Date:	Sat, 19 Jan 2008 11:45:35 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	salikhmetov@...il.com
CC:	miklos@...redi.hu, linux-mm@...ck.org, jakob@...hought.net,
	linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
	riel@...hat.com, ksm@...dk, staubach@...hat.com,
	jesper.juhl@...il.com, torvalds@...ux-foundation.org,
	a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	protasnb@...il.com, r.e.wolff@...wizard.nl,
	hidave.darkstar@...il.com, hch@...radead.org
Subject: Re: [PATCH -v6 0/2] Fixing the issue with memory-mapped file times

> 2008/1/18, Miklos Szeredi <miklos@...redi.hu>:
> > > 4. Performance test was done using the program available from the
> > > following link:
> > >
> > > http://bugzilla.kernel.org/attachment.cgi?id=14493
> > >
> > > Result: the impact of the changes was negligible for files of a few
> > > hundred megabytes.
> >
> > Could you also test with ext4 and post some numbers?  Afaik, ext4 uses
> > nanosecond timestamps, so the time updating code would be exercised
> > more during the page faults.
> >
> > What about performance impact on msync(MS_ASYNC)?  Could you please do
> > some measurment of that as well?
> 
> Did a quick test on an ext4 partition. This is how it looks like:

Thanks for running these tests.

I was more interested in the slowdown on ext4 (checked with the above
mentioned program).  Can you do such a test as well, and post
resulting times with and without the patch?

> Table 1. Reference platforms.
> 
> ------------------------------------------------------------
> |             | HP-UX/PA-RISC | HP-UX/Itanium | FreeBSD    |
> ------------------------------------------------------------
> | First run   | 263405 usec   | 202283 usec   | 90 SECONDS |
> ------------------------------------------------------------
> | Second run  | 262253 usec   | 172837 usec   | 90 SECONDS |
> ------------------------------------------------------------
> | Third run   | 238465 usec   | 238465 usec   | 90 SECONDS |
> ------------------------------------------------------------
> 
> It looks like FreeBSD is a clear outsider here. Note that FreeBSD
> showed an almost liner depencence of the time spent in the
> msync(MS_ASYNC) call on the file size.
> 
> Table 2. The Qemu system. File size is 512M.
> 
> ---------------------------------------------------
> |            | Before the patch | After the patch |
> ---------------------------------------------------
> | First run  |     35 usec      |   5852 usec     |
> ---------------------------------------------------
> | Second run |     35 usec      |   4444 usec     |
> ---------------------------------------------------
> | Third run  |     35 usec      |   6330 usec     |
> ---------------------------------------------------

Interesting.

Thanks,
Miklos
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