From: Andi Kleen <andi@firstfloor.org>
To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Slowdown due to threads bouncing between HT cores
Date: Sat, 04 Oct 2014 06:41:15 -0700 [thread overview]
Message-ID: <87a95cq7es.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <20141003194428.GA27084@sesse.net> (Steinar H. Gunderson's message of "Fri, 3 Oct 2014 21:44:29 +0200")
"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
>
> So, benchmark:
>
> - Default: 13266 kN/sec
> - Change from ondemand to performance on all cores: 14600 kN/sec
> - taskset -c 0-19 (locking affinity to only one set of hyperthreads):
> 17512 kN/sec
iirc the main reasons for unbound threads migrating away are:
- something else gets scheduled on these logical CPUs, so
the scheduler tries to balance to run queue lengths
You could check that with perf timechart or perf sched record/map
or kernelshark.
- there is some IO or communication which causes wakeup affinity.
You could try disabling WAKEUP_PREEMPTION or NEXT_BUDDY in
/sys/kernel/debug/sched_features
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2014-10-04 13:41 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-03 19:44 Slowdown due to threads bouncing between HT cores Steinar H. Gunderson
2014-10-03 21:11 ` Marc Burkhardt
2014-10-03 21:14 ` Steinar H. Gunderson
2014-10-04 9:22 ` Marc Burkhardt
2014-10-04 13:41 ` Andi Kleen [this message]
2014-10-04 14:12 ` Steinar H. Gunderson
2014-10-04 14:50 ` Chuck Ebbert
2014-10-05 11:19 ` Steinar H. Gunderson
2014-10-08 15:37 ` bisected: futex regression >= 3.14 - was - " Mike Galbraith
2014-10-08 16:14 ` Thomas Gleixner
2014-10-08 16:45 ` Steinar H. Gunderson
2014-10-08 17:52 ` Mike Galbraith
2014-10-08 16:23 ` Steinar H. Gunderson
2014-10-08 17:04 ` Linus Torvalds
2014-10-08 17:05 ` Steinar H. Gunderson
2014-10-08 17:59 ` Mike Galbraith
2014-10-24 15:25 ` Thomas Gleixner
2014-10-24 16:38 ` Mike Galbraith
2014-10-26 10:39 ` Steinar H. Gunderson
2014-10-26 13:16 ` Mike Galbraith
2014-10-26 13:58 ` Mike Galbraith
2014-10-26 14:11 ` Steinar H. Gunderson
2014-10-26 14:41 ` Mike Galbraith
2014-10-27 10:05 ` Mike Galbraith
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