linux-kernel - Re: [RFC] sched: The removal of idle

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Date:	Fri, 15 Feb 2013 08:26:12 +0100
From:	Mike Galbraith <efault@....de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Clark Williams <clark@...hat.com>,
	Andrew Theurer <habanero@...ibm.com>
Subject: Re: [RFC] sched: The removal of idle_balance()

On Fri, 2013-02-15 at 01:13 -0500, Steven Rostedt wrote:

> Think about it some more, just because we go idle isn't enough reason to
> pull a runable task over. CPUs go idle all the time, and tasks are woken
> up all the time. There's no reason that we can't just wait for the sched
> tick to decide its time to do a bit of balancing. Sure, it would be nice
> if the idle CPU did the work. But I think that frame of mind was an
> incorrect notion from back in the early 2000s and does not apply to
> today's hardware, or perhaps it doesn't apply to the (relatively) new
> CFS scheduler. If you want aggressive scheduling, make the task rt, and
> it will do aggressive scheduling.

(the throttle is supposed to keep idle_balance() from doing severe
damage, that may want a peek/tweak)

Hackbench spreads itself with FORK/EXEC balancing, how does say a kbuild
do with no idle_balance()?

-Mike

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