linux-kernel - Re: [RFC PATCH 0/3] CFS idle injection

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Date:	Mon, 9 Nov 2015 06:36:51 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Punit Agrawal <punit.agrawal@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Eduardo Valentin <edubezval@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH 0/3] CFS idle injection

On Mon, 09 Nov 2015 11:56:51 +0000
Punit Agrawal <punit.agrawal@....com> wrote:

> > actually, I was suggesting to start considering idle injection once
> > frequency capped to the energy efficient point, which can be much
> > higher than the lowest frequency. The idea being, deep idle power is
> > negligible compared to running power which allows near linear
> > power-perf scaling for balanced workload.
> > Below energy efficient frequency, continuous lowering frequency may
> > lose disproportion performance vs. power. i.e. worse than linear.
> >  
> 
> I agree. I was making that assumption that with the ability to inject
> idle states, there wouldn't be a need to expose the inefficient
> frequency states.
> 
> Do you still see a reason to do that?
yes, but it is up to a governor or management sw to decide when to to
pick what mechanism. there may be certain workload scale better with
frequency change. e.g. unbalanced workload, we don't want to inject
idle to all cpus if just one is busy. but it is also unlikely to run
into thermal issue in this case.
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