linux-kernel - Re: [PATCH RFC] sched,idle: teach select_idle

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Message-ID: <1412316263.5149.9.camel@marge.simpson.net>
Date:	Fri, 03 Oct 2014 08:04:23 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH RFC] sched,idle: teach select_idle_sibling about idle
 states

On Thu, 2014-10-02 at 13:15 -0400, Rik van Riel wrote:

> This patch is ugly. I have not bothered cleaning it up, because it
> causes a regression with hackbench. Apparently for hackbench (and
> potentially other sync wakeups), locality is more important than
> idleness.
> 
> We may need to add a third clause before the search, something
> along the lines of, to ensure target gets selected if neither
> target or i are idle and the wakeup is synchronous...
> 
>     if (sync_wakeup && cpu_of(target)->nr_running == 1)
> 	return target;

I recommend you forget that trusting sync hint ever sprang to mind, it
is often a big fat lie.

-Mike

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