linux-kernel - Re: [RFC PATCHC 0/3] sched/idle : find the idlest cpu with cpuidle info

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Message-ID: <2100495.CxRsoJUgjf@vostro.rjw.lan>
Date:	Tue, 15 Apr 2014 17:33:20 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	linux-pm@...r.kernel.org, alex.shi@...aro.org,
	vincent.guittot@...aro.org, morten.rasmussen@....com
Subject: Re: [RFC PATCHC 0/3] sched/idle : find the idlest cpu with cpuidle info

On Tuesday, April 15, 2014 03:25:10 PM Peter Zijlstra wrote:
> On Fri, Apr 04, 2014 at 01:43:00PM +0200, Rafael J. Wysocki wrote:
> > > That's what this patch series is about.  The find_idlest_cpu code should 
> > > look for the idle CPU with the shallowest idle state, or the one with 
> > > the smallest load.  In this context "find_idlest_cpu" might become a 
> > > misnomer.
> > 
> > Yes, clearly.  It should be called find_best_cpu or something like that.
> 
> Ha!, but for what purpose? We already have find_busiest_cpu() to find
> the CPU to steal work from. The converse action, currently called
> find_idlest_cpu() is finding the CPU where to put work.
> 
> 'Best' is ambiguous in all regards, it doesn't convey the direction nor
> the quality sorted on.
> 
> So while idlest might be somewhat of a misnomer, it at least conveys the
> directional thing fairly well. Also we are still searching the least
> busy, and preferable an idle, cpu. 'Idlest' being a superlative also
> conveys the meaning of order.

But 'idlest' can also be understood as 'deepest idle', which clearly is not the
intent.  Perhaps find_cpu_for_work() reflects what it does, but I'm not sure
if that's a good name either.

Rafael

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