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

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Date:	Mon, 19 Nov 2012 23:48:47 -0800
From:	Paul Turner <pjt@...gle.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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

On Mon, Nov 19, 2012 at 11:44 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * David Rientjes <rientjes@...gle.com> wrote:
>
>> On Tue, 20 Nov 2012, Ingo Molnar 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.
>> >
>>
>> This happened to be an Opteron (but not 83xx series), 2.4Ghz.
>
> Ok - roughly which family/model from /proc/cpuinfo?
>
>> Your benchmarks were different in the number of cores but also
>> in the amount of memory, do you think numa/core would regress
>> because this is 32GB and not 64GB?
>
> I'd not expect much sensitivity to RAM size.
>
>> > (A wild guess would be an older 4x Opteron system, 83xx
>> > series or so?)
>>
>> Just curious, how you would guess that? [...]
>
> I'm testing numa/core on many systems and the performance
> figures seemed to roughly map to that range.
>
>> [...]  Is there something about Opteron 83xx that make
>> numa/core regress?
>
> Not that I knew of - but apparently there is! I'll try to find a
> system that matches yours as closely as possible and have a
> look.

Here I'd note the node-distances that David included above.  This
system is not fully connected, having an (asymmetric) kite topology.
Only nodes nodes 1 and 2 are fully connected.

This is sufficiently whacky that it seems a likely candidate :-).

- Paul

>
>> > 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:
>> >
>>
>> It's perf top -U, the benchmark itself was unchanged so I
>> didn't think it was interesting to gather the user symbols.
>> If that would be helpful, let me know!
>
> Yeah, regular perf top output would be very helpful to get a
> general sense of proportion. Thanks!
>
>         Ingo
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