linux-kernel - Re: [PATCH 00/27] Latest numa/core release, v16

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Date:	Tue, 20 Nov 2012 07:00:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 00/27] Latest numa/core release, v16


* David Rientjes <rientjes@...gle.com> wrote:

> > numa/core at ec05a2311c35 ("Merge branch 'sched/urgent' into 
> > sched/core") had an average throughput of 136918.34 
> > SPECjbb2005 bops, which is a 6.3% regression.
> 
> perftop during the run on numa/core at 01aa90068b12 ("sched: 
> Use the best-buddy 'ideal cpu' in balancing decisions"):
> 
>     15.99%  [kernel]  [k] page_fault                         
>      4.05%  [kernel]  [k] getnstimeofday                     
>      3.96%  [kernel]  [k] _raw_spin_lock                     
>      3.20%  [kernel]  [k] rcu_check_callbacks                
>      2.93%  [kernel]  [k] generic_smp_call_function_interrupt
>      2.90%  [kernel]  [k] __do_page_fault                    
>      2.82%  [kernel]  [k] ktime_get                          

Thanks for testing, that's very interesting - could you tell me 
more about exactly what kind of hardware this is? I'll try to 
find a similar system and reproduce the performance regression.

(A wild guess would be an older 4x Opteron system, 83xx series 
or so?)

Also, the profile looks weird to me. Here is how perf top looks 
like on my system during a similarly configured, "healthy" 
SPECjbb run:

 91.29%  perf-6687.map            [.] 0x00007fffed1e8f21
  4.81%  libjvm.so                [.] 0x00000000007004a0
  0.93%  [vdso]                   [.] 0x00007ffff7ffe60c
  0.72%  [kernel]                 [k] do_raw_spin_lock
  0.36%  [kernel]                 [k] generic_smp_call_function_interrupt
  0.10%  [kernel]                 [k] format_decode
  0.07%  [kernel]                 [k] rcu_check_callbacks
  0.07%  [kernel]                 [k] apic_timer_interrupt
  0.07%  [kernel]                 [k] call_function_interrupt
  0.06%  libc-2.15.so             [.] __strcmp_sse42
  0.06%  [kernel]                 [k] irqtime_account_irq
  0.06%  perf                     [.] 0x000000000004bb7c
  0.05%  [kernel]                 [k] x86_pmu_disable_all
  0.04%  libc-2.15.so             [.] __memcpy_ssse3
  0.04%  [kernel]                 [k] ktime_get
  0.04%  [kernel]                 [k] account_group_user_time
  0.03%  [kernel]                 [k] vbin_printf

and that is what SPECjbb does: it spends 97% of its time in Java 
code - yet there's no Java overhead visible in your profile - 
how is that possible? Could you try a newer perf on that box:

  cd tools/perf/
  make -j install

to make sure perf picks up the Java symbols as well (or at least 
includes them as a summary, as in the profile above). Note that 
no page fault overhead is visible in my profile.

Thanks,

	Ingo
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