Date: Mon, 9 Nov 2015 15:15:34 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Punit Agrawal <punit.agrawal@arm.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>, Paul Turner <pjt@google.com>,
        Len Brown <len.brown@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andi Kleen <andi.kleen@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>
Subject: Re: [RFC PATCH 0/3] CFS idle injection
Message-ID: <20151109141534.GL17308@twins.programming.kicks-ass.net>
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On Mon, Nov 09, 2015 at 11:56:51AM +0000, Punit Agrawal wrote:
> Jacob Pan <jacob.jun.pan@linux.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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