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

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Message-ID: <20151109141534.GL17308@twins.programming.kicks-ass.net>
Date:	Mon, 9 Nov 2015 15:15:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Punit Agrawal <punit.agrawal@....com>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	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>
Subject: Re: [RFC PATCH 0/3] CFS idle injection

On Mon, Nov 09, 2015 at 11:56:51AM +0000, Punit Agrawal wrote:
> Jacob Pan <jacob.jun.pan@...ux.intel.com> writes:
> > My take is that RT and throttling will never go well together since they
> > are conflicting in principle.
> 
> I am not sure I follow. If RT (or other higher priority classes) can't
> be throttled then the CPUs are not able to contribute towards
> constraining power consumption and hence temperature.
> 
> This is especially true in certain platforms where tasks belong to the
> RT class to maintain user experience, e.g., audio and video. 

Audio/Video playback generally doesn't take a _lot_ of time these days.
What is important though is _when_ it happens.

And media playback typically already has a very well defined and stable
cadence (24Hz or whatnot).  What you want is for your idle injector to
sync up with that, not disrupt it.

For other workloads, missing a deadline is about as bad as destroying
the chip, complete system shutdown might be safer than getting delayed.
(The very tired scenario of a saw, a laser and your finger; you want to
shut down the entire machine rather than just cut off your finger.)



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