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Date: Sun, 14 Jul 2002 23:52:25 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Lincoln Dale <ltd@cisco.com>
CC: Benjamin LaHaise <bcrl@redhat.com>, Andrea Arcangeli <andrea@suse.de>,
       "Stephen C. Tweedie" <sct@redhat.com>,
       Linus Torvalds <torvalds@transmeta.com>, Steve Lord <lord@sgi.com>,
       linux-kernel@vger.kernel.org
Subject: Re: ext2 performance in 2.5.25 versus 2.4.19pre8aa2
References: <3D325DEB.A9920C12@zip.com.au> <5.1.0.14.2.20020715160245.02ad0978@mira-sjcm-3.cisco.com>
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Lincoln Dale wrote:
> 
> At 10:30 PM 14/07/2002 -0700, Andrew Morton wrote:
> >Funny thing about your results is the presence of sched_yield(),
> >especially in the copy-from-pagecache-only load.  That test should
> >peg the CPU at 100% and definitely shouldn't be spending time in
> >default_idle.  So who is calling sched_yield()?  I think it has to be
> >your test app?
> >
> >Be aware that the sched_yield() behaviour in 2.5 has changed a lot
> >wrt 2.4.  It has made StarOffice 5.2 completely unusable on a non-idle
> >system, for a start.  (This is a SO problem and not a kernel problem,
> >but it's a lesson).
> 
> my test app uses pthreads (one thread per disk-worker) and
> pthread_cond_wait in the master task to wait for all workers to finish.
> i'll switch the app to use clone() and sys_futex instead.

OK.

> i guess in that case, its debatable whether its a kernel problem or not --
> pthreads is out there, and if its default behavior is bad, any threaded app
> which uses it will also be bad.

Well if your machine is executing a single cycle in default_idle
with that load then there's a bug somewhere.

I took a quick look at glibc-linuxthreads but as usual, my brain
turned to mush and it took seven years off my life.

If you can send me a copy of your test app I'll take a look
at what's going on.

Thanks.
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