From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Slowdown due to threads bouncing between HT cores
Date: Sun, 5 Oct 2014 13:19:11 +0200 [thread overview]
Message-ID: <20141005111911.GA35329@sesse.net> (raw)
In-Reply-To: <20141004095004.3b84095f@as>
On Sat, Oct 04, 2014 at 09:50:04AM -0500, Chuck Ebbert wrote:
> 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.
I can't get any good effect out of this. I tried both 50 ms (your value) and
500 ms, and while it seems (by eyeballing the per-cpu display in top) to
_sometimes_ lock the processes to cores, more often than not, they still
bounce around between all 40. Worse still, when it _does_, it seems to often
lock them to hyperthread pairs (e.g., I've seen it put threads only on
virtual cores 0-9 and 20-29, which means it has all of them on one socket!)
Notwithstanding top, the benchmarks don't improve; setting cores manually
with taskset still is much better.
/* Steinar */
--
Homepage: http://www.sesse.net/
next prev parent reply other threads:[~2014-10-05 11:19 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
2014-10-05 11:19 ` Steinar H. Gunderson [this message]
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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