linux-kernel - Re: bisected: futex regression >= 3.14 - was - Slowdown due to threads bouncing between HT cores

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Message-ID: <1414329375.5304.20.camel@marge.simpson.net>
Date:	Sun, 26 Oct 2014 14:16:15 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	"Steinar H. Gunderson" <sgunderson@...foot.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: bisected: futex regression >= 3.14 - was - Slowdown due to
 threads bouncing between HT cores

On Sun, 2014-10-26 at 11:39 +0100, Steinar H. Gunderson wrote: 
> On Fri, Oct 24, 2014 at 06:38:41PM +0200, Mike Galbraith wrote:
> >>> Whew, good, futex.c is hard.  Heads up chess guys <punt>. 
> >> I wonder whether the barrier fix which got into 3.17 late fixes that
> >> issue as well.
> > Yes, it did.
> 
> This is only about the lockup, right, not that the threads bounce around a
> lot and make things slower?

Yes.  I couldn't reproduce your results, on my 28 core+ht box, there was
little difference between pinned/unpinned.  Maybe the box was too quite,
not enough random activity to motivate select_idle_sibling().

-Mike

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