linux-kernel - Re: [cgroup] a0f9ec1f181: -4.3% will-it-scale.per_thread

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Date:	Thu, 15 May 2014 09:11:17 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Jet Chen <jet.chen@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [cgroup] a0f9ec1f181: -4.3% will-it-scale.per_thread_ops

On Thu, 2014-05-15 at 02:14 -0400, Tejun Heo wrote:

> Hmmm... I'm completely stumped.  The commit in question has nothing to
> do with tmpfs.  It only affects three cgroup files - "tasks",
> "cgroup.procs" and "release_agent".  It can't possibly have any effect
> on tmpfs operation.  Maybe random effect through code alignment?  Even
> that is highly unlikely.

Unlikely, but it happens.  I bisected a tbench regression down to a
completely unrelated driver change, and watched it repeatably drop
throughput 5% despite skeptical "No way, show me that trick again".

-Mike

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