linux-kernel - Re: 2.6.36 io bring the system to its knees

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Date:	Thu, 28 Oct 2010 18:18:05 +0600
From:	Aidar Kultayev <the.aidar@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, npiggin@...nel.dk,
	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 2.6.36 io bring the system to its knees

http://picasaweb.google.com/aidar.eiei/LinuxIo#5533068249408411698

I will look into latencytop output and will figure out a usage pattern
that is most annoying with regards to IO.
Will try to see what leads to that & if possible to make a screenshot
of what is going on.
The thing is, I don't think the program that captures the screenshots
does it in a meaningful way, because at the moment the system is
brought to its knees, I don't think that this particular program
(KSnapshot) can get away from being affected. I mean it might take a
snapshot which is not representative enough.


thanks, Aidar

On Thu, Oct 28, 2010 at 5:48 PM, Pekka Enberg <penberg@...nel.org> wrote:
> On Thu, Oct 28, 2010 at 2:33 PM, Aidar Kultayev <the.aidar@...il.com> wrote:
>> if it wasn't picasa, it would have been something else. I mean if I
>> kill picasa ( later on it was done indexing new pics anyway ), it
>> would have been for virtualbox to thrash the io. So, nope, getting rid
>> of picasa doesn't help either. In general the systems responsiveness
>> or sluggishness is dominated by those io operations going on - the DD
>> & CP & probably VBOX issuing whole bunch of its load for IO.
>
> Do you still see high latencies in vfs_lseek() and vfs_fsync()? I'm
> not a VFS expert but looking at your latencytop output, it seems that
> fsync grabs ->i_mutex which blocks vfs_llseek(), for example. I'm not
> sure why that causes high latencies though it's a mutex we're holding.
>
> On Thu, Oct 28, 2010 at 2:33 PM, Aidar Kultayev <the.aidar@...il.com> wrote:
>> Another way I see these delays, is when I leave system overnight, with
>> ktorrent & juk(stopped) in the background. It takes some time for
>> WM(kwin) to work out ALT+TAB the very next morning. But this might be
>> because the WM(kwin & its code) has been swapped out, because of long
>> period of not using it.
>
> Yeah, that's probably paging overhead.
>
> P.S. Can you please upload latencytop output somewhere and post an URL
> to it so other people can also see it?
>
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