From: Ingo Molnar <mingo@kernel.org>
To: lkp@lists.01.org
Subject: Re: [sched/numa] 096aa33863a: -21.4% hackbench.throughput, -20.2% netperf.Throughput_Mbps
Date: Fri, 08 Aug 2014 10:38:53 +0200 [thread overview]
Message-ID: <20140808083853.GA8919@gmail.com> (raw)
In-Reply-To: <53E3C270.1010302@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 1496 bytes --]
* Rik van Riel <riel@redhat.com> wrote:
> On 08/07/2014 06:53 AM, Fengguang Wu wrote:
> > Hi Rik,
> >
> > We noticed the below performance regression in commit
> > 096aa33863a5e48de52d2ff30e0801b7487944f4 ("sched/numa: Decay
> > ->wakee_flips instead of zeroing")
> >
> > b1ad065e65f5610 096aa33863a5e48de52d2ff30 testbox/testcase/testparams
> > --------------- ------------------------- ---------------------------
> > 122361 ± 0% -21.4% 96140 ± 0% lkp-snb01/hackbench/50%-process-pipe
> > 122361 ± 0% -21.4% 96140 ± 0% TOTAL hackbench.throughput
>
> I guess the performance of that benchmark depends on it
> "slipping under the wire" after each time the kernel
> zeroes out ->wakee_flips.
>
> Depending on repeatedly pulling the wakee back to the same
> node as the waker suggests something else in the kernel may
> be pulling the wakee to another place in the system repeatedly,
> as well, just at a lower frequency (load balancer?).
>
> I have also noticed that select_idle_sibling often fails to
> find an idle sibling within the LLC domain, even when it
> exists. Fixing that bug sometimes results in lower performance.
>
> It appears that some of the performance results of the scheduler
> appear on the code acting in an opposite way to its documented
> intention.
>
> It may be best to revert 096aa33863a for now...
Mind sending a revert patch, with an explanation, a Reported-by, etc?
Thanks,
Ingo
WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@elte.hu>,
LKML <linux-kernel@vger.kernel.org>,
lkp@01.org, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [sched/numa] 096aa33863a: -21.4% hackbench.throughput, -20.2% netperf.Throughput_Mbps
Date: Fri, 8 Aug 2014 10:38:53 +0200 [thread overview]
Message-ID: <20140808083853.GA8919@gmail.com> (raw)
In-Reply-To: <53E3C270.1010302@redhat.com>
* Rik van Riel <riel@redhat.com> wrote:
> On 08/07/2014 06:53 AM, Fengguang Wu wrote:
> > Hi Rik,
> >
> > We noticed the below performance regression in commit
> > 096aa33863a5e48de52d2ff30e0801b7487944f4 ("sched/numa: Decay
> > ->wakee_flips instead of zeroing")
> >
> > b1ad065e65f5610 096aa33863a5e48de52d2ff30 testbox/testcase/testparams
> > --------------- ------------------------- ---------------------------
> > 122361 ± 0% -21.4% 96140 ± 0% lkp-snb01/hackbench/50%-process-pipe
> > 122361 ± 0% -21.4% 96140 ± 0% TOTAL hackbench.throughput
>
> I guess the performance of that benchmark depends on it
> "slipping under the wire" after each time the kernel
> zeroes out ->wakee_flips.
>
> Depending on repeatedly pulling the wakee back to the same
> node as the waker suggests something else in the kernel may
> be pulling the wakee to another place in the system repeatedly,
> as well, just at a lower frequency (load balancer?).
>
> I have also noticed that select_idle_sibling often fails to
> find an idle sibling within the LLC domain, even when it
> exists. Fixing that bug sometimes results in lower performance.
>
> It appears that some of the performance results of the scheduler
> appear on the code acting in an opposite way to its documented
> intention.
>
> It may be best to revert 096aa33863a for now...
Mind sending a revert patch, with an explanation, a Reported-by, etc?
Thanks,
Ingo
next prev parent reply other threads:[~2014-08-08 8:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-07 10:53 [sched/numa] 096aa33863a: -21.4% hackbench.throughput, -20.2% netperf.Throughput_Mbps Fengguang Wu
2014-08-07 10:53 ` Fengguang Wu
2014-08-07 18:16 ` Rik van Riel
2014-08-07 18:16 ` Rik van Riel
2014-08-08 8:38 ` Ingo Molnar [this message]
2014-08-08 8:38 ` Ingo Molnar
2014-08-11 14:17 ` Peter Zijlstra
2014-08-11 14:17 ` Peter Zijlstra
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