linux-kernel - Re: [PATCH 3/4] sched: introduce synchronized idle injection

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Message-ID: <564C9E93.8030901@linux.intel.com>
Date:	Wed, 18 Nov 2015 07:51:47 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Morten Rasmussen <morten.rasmussen@....com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection

On 11/18/2015 7:44 AM, Morten Rasmussen wrote:
> I would not necessarily want to punish all cpus
> system-wide if we have local overheating in one corner. If would rather
> have it apply to only the overheating socket in a multi-socket machine
> and only the big cores in a big.LITTLE system.

most of the time thermal issues aren't inside the SOC, but on a system level
due to cheap heat spreaders or outright lack of space due to thinness. But
even if you have one part of the die too hot:

For core level idle injection, no need to synchronize that; the reason to synchronize
is generally that when ALL cores are idle, additional power savings kick in
(like memory going to self refresh, fabrics power gating etc); those additional
power savings are what makes this more efficient than just voltage/frequency
scaling at the bottom of that range...   not so much the fact that things are just idle.

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