linux-kernel - Re: sched: Avoid SMT siblings in select_idle

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Message-ID: <1332856598.7425.25.camel@marge.simpson.net>
Date:	Tue, 27 Mar 2012 15:56:38 +0200
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>
Subject: Re: sched: Avoid SMT siblings in select_idle_sibling() if possible

On Mon, 2012-03-26 at 20:06 +0200, Peter Zijlstra wrote:

> The biggest regression came from tbench, wasn't that mostly a random
> number generator anyway?

That's dbench ;-)  Tbench does wiggle around more than you'd like
though.  I've never tracked, but in lots of running the thing, 2-3% you
can forget chasing, and I once bisected a 5% regression to an unrelated
change, reverted and re-applied the suspect a few times in disbelief,
and it tracked.  You can't trust it _too_ much.  I consider it a
reliable indicator that I'd better do more testing.  If others agree,
it's a real regression, if not, it's those damn Elves 'n Gremlins ;-)

-Mike

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