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 20:17:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Anton Starikov <ant.starikov@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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
Subject: Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge
 regression in performance

On Tue, 2010-03-23 at 20:14 +0100, Anton Starikov wrote:
> 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.
> 
> 
> Applied mentioned patches. Things didn't improve too much.
> 
> before:
> prog: Total exploration time 9.880 real 60.620 user 76.970 sys
> 
> after:
> prog: Total exploration time 9.020 real 59.430 user 66.190 sys
> 
> perf report:
> 
>     38.58%             prog  [kernel]                                           [k] _spin_lock_irqsave
>     37.42%             prog  ./prog                                             [.] DBSLLlookup_ret
>      6.22%             prog  ./prog                                             [.] SuperFastHash
>      3.65%             prog  /lib64/libc-2.11.1.so                              [.] __GI_memcpy
>      2.09%             prog  ./anderson.6.dve2C                                 [.] get_successors
>      1.75%             prog  [kernel]                                           [k] clear_page_c
>      1.73%             prog  ./prog                                             [.] index_next_dfs
>      0.71%             prog  [kernel]                                           [k] handle_mm_fault
>      0.38%             prog  ./prog                                             [.] cb_hook
>      0.33%             prog  ./prog                                             [.] get_local
>      0.32%             prog  [kernel]                                           [k] page_fault

Could you verify with a callgraph profile what that spin_lock_irqsave()
is? If those rwsem patches were successfull mmap_sem should no longer
have a spinlock to content on, in which case it might be another lock.

If not, something went wrong with backporting those patches.
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