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Message-ID: <20100323180002.GA2965@elte.hu>
Date: Tue, 23 Mar 2010 19:00:02 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
bugme-daemon@...zilla.kernel.org, ant.starikov@...il.com,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge
regression in performance
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Tue, 23 Mar 2010, Ingo Molnar wrote:
> >
> > It shows a very brutal amount of page fault invoked mmap_sem spinning
> > overhead.
>
> Isn't this already fixed? It's the same old "x86-64 rwsemaphores are using
> the shit-for-brains generic version" thing, and it's fixed by
>
> 1838ef1 x86-64, rwsem: 64-bit xadd rwsem implementation
> 5d0b723 x86: clean up rwsem type system
> 59c33fa x86-32: clean up rwsem inline asm statements
Ah, indeed!
> NOTE! None of those are in 2.6.33 - they were merged afterwards. But they
> are in 2.6.34-rc1 (and obviously current -git). So Anton would have to
> compile his own kernel to test his load.
another option is to run the rawhide kernel via something like:
yum update --enablerepo=development kernel
this will give kernel-2.6.34-0.13.rc1.git1.fc14.x86_64, which has those
changes included.
OTOH that kernel has debugging [lockdep] enabled so it might not be
comparable.
> We could mark them as stable material if the load in question is a real load
> rather than just a test-case. On one of the random page-fault benchmarks the
> rwsem fix was something like a 400% performance improvement, and it was
> apparently visible in real life on some crazy SGI "initialize huge heap
> concurrently on lots of threads" load.
>
> Side note: the reason the spinlock sucks is because of the fair ticket
> locks, it really does all the wrong things for the rwsem code. That's why
> old kernels don't show it - the old unfair locks didn't show the same kind
> of behavior.
Yeah.
Ingo
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