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

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Date:	Sun, 17 Feb 2013 08:14:05 +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 Sun, 2013-02-17 at 07:26 +0100, Mike Galbraith wrote: 
> On Sat, 2013-02-16 at 11:12 -0500, Steven Rostedt wrote:
> > On Fri, 2013-02-15 at 08:26 +0100, Mike Galbraith wrote:
> > > 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()?
> > > 
> > 
> > Interesting, I added this patch and it brought down my hackbench to the
> > same level as removing idle_balance().
> 
> The typo did it's job well :)
> 
> Hrm, turning idle balancing off here does not help hackbench at all.

(And puts a dent in x264 ultrafast)

+SD_BALANCE_NEWIDLE
encoded 600 frames, 425.04 fps, 22132.71 kb/s
encoded 600 frames, 416.07 fps, 22132.71 kb/s
encoded 600 frames, 417.49 fps, 22132.71 kb/s
encoded 600 frames, 420.65 fps, 22132.71 kb/s
encoded 600 frames, 425.55 fps, 22132.71 kb/s
encoded 600 frames, 425.58 fps, 22132.71 kb/s
encoded 600 frames, 426.18 fps, 22132.71 kb/s
encoded 600 frames, 424.21 fps, 22132.71 kb/s
encoded 600 frames, 422.20 fps, 22132.71 kb/s
encoded 600 frames, 423.15 fps, 22132.71 kb/s

-SD_BALANCE_NEWIDLE
encoded 600 frames, 378.52 fps, 22132.71 kb/s
encoded 600 frames, 378.75 fps, 22132.71 kb/s
encoded 600 frames, 378.20 fps, 22132.71 kb/s
encoded 600 frames, 372.54 fps, 22132.71 kb/s
encoded 600 frames, 366.69 fps, 22132.71 kb/s
encoded 600 frames, 378.46 fps, 22132.71 kb/s
encoded 600 frames, 379.89 fps, 22132.71 kb/s
encoded 600 frames, 382.25 fps, 22132.71 kb/s
encoded 600 frames, 384.10 fps, 22132.71 kb/s
encoded 600 frames, 375.24 fps, 22132.71 kb/s



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