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Subject: Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance
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From: Anton Starikov <ant.starikov@gmail.com>
In-Reply-To: <alpine.LFD.2.00.1003231037410.18017@i5.linux-foundation.org>
Date: Tue, 23 Mar 2010 20:14:48 +0100
Cc: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
       linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       bugzilla-daemon@bugzilla.kernel.org, bugme-daemon@bugzilla.kernel.org,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
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References: <bug-15618-10286@https.bugzilla.kernel.org/> <20100323102208.512c16cc.akpm@linux-foundation.org> <20100323173409.GA24845@elte.hu> <alpine.LFD.2.00.1003231037410.18017@i5.linux-foundation.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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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

Anton.