From: Chuck Ebbert <cebbert.lkml@gmail.com>
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, 4 Oct 2014 09:50:04 -0500 [thread overview]
Message-ID: <20141004095004.3b84095f@as> (raw)
In-Reply-To: <20141003194428.GA27084@sesse.net>
On Fri, 3 Oct 2014 21:44:29 +0200
"Steinar H. Gunderson" <sgunderson@bigfoot.com> wrote:
> Hi,
>
> I did a chess benchmark of my new machine (2x E5-2650v3, so 20x2.3GHz
> Haswell-EP), and it performed a bit worse than comparable Windows setups.
> It looks like the scheduler somehow doesn't perform as well with
> hyperthreading; HT is on in the BIOS, but I'm only using 20 threads
> (chess scales sublinearly, so using all 40 usually isn't a good idea),
> so really, the threads should just get one core each and that's it.
> It looks like they are bouncing between cores, reducing overall performance
> by ~20% for some reason. (The machine is otherwise generally idle.)
>
Try playing with /proc/sys/kernel/sched_migration_cost_ns. This sets
the number of nanoseconds the kernel will wait before considering
moving a thread to another CPU. I have mine set to 50000000.
next prev parent reply other threads:[~2014-10-04 14:50 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
2014-10-04 14:12 ` Steinar H. Gunderson
2014-10-04 14:50 ` Chuck Ebbert [this message]
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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