linux-kernel - Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq

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Date:	Fri, 22 Feb 2013 15:42:22 +0100
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, alex.shi@...el.com,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

On Fri, 2013-02-22 at 15:30 +0100, Mike Galbraith wrote: 
> On Fri, 2013-02-22 at 14:06 +0100, Ingo Molnar wrote: 

> > I think it might be better to measure the scheduling rate all 
> > the time, and save the _shortest_ cross-cpu-wakeup and 
> > same-cpu-wakeup latencies (since bootup) as a reference number. 
> > 
> > We might be able to pull this off pretty cheaply as the 
> > scheduler clock is running all the time and we have all the 
> > timestamps needed.
> 
> Yeah, that might work.  We have some quick kthreads, so saving ctx
> distance may get close enough to scheduler cost to be good enough.

Or better, shortest idle to idle, that would include the current (bad)
nohz cost, and automatically shrink away when that cost shrinks.

-Mike

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