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

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Message-ID: <20151106111838.6172085d@icelake>
Date:	Fri, 6 Nov 2015 11:18:38 -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 Fri, 06 Nov 2015 16:50:15 +0000
Punit Agrawal <punit.agrawal@....com> wrote:

> * idle injection once frequencies have been capped to the lowest
>   feasible values (as suggested in the cover letter)
> 
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.

> One question about the implementation in these patches - should the
> implementation hook into pick_next_task in core instead of CFS? Higher
> priority tasks might get in the way of idle injection.
My take is that RT and throttling will never go well together since they
are conflicting in principle.
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