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

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Date:	Mon, 9 Nov 2015 22:45:12 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Dietmar Eggemann <dietmar.eggemann@....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 01:23:04PM -0800, Jacob Pan wrote:
> what is WFI?

Wait For Interrupt; very like the x86 HLT thing.

> For Intel, idle states are hints to the HW. The FW decides how far the
> idle can go based on many factors, device states included, some are
> visible to the OS some are not. We just to help mature such deep idle
> conditions.

On some ARM you have to manually orchestrate cluster idle, which is
clustered idle states in cpuidle. The up-side is that you explicitly
know about them, the down side is that its cross CPU bits and a freak
show (think doing cross CPU atomics while a CPU isn't in the coherency
domain yet).
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