linux-kernel - Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance

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Date:	Tue, 23 Mar 2010 18:57:34 +0100
From:	Anton Starikov <ant.starikov@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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,
	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


On Mar 23, 2010, at 6:45 PM, Linus Torvalds 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
> 
> 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.

Thanks for info, I will try it now.

> 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.

It is not just a test-case, it is real-life code. With real-life problems on 2.6.32 and later :)


Anton.--
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