Date: Mon, 9 Nov 2015 22:45:12 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.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: <20151109214512.GN17308@twins.programming.kicks-ass.net>
References: <1446509428-5616-1-git-send-email-jacob.jun.pan@linux.intel.com>
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 <20151104085830.010e69f8@yairi>
 <20151105101218.GB3604@twins.programming.kicks-ass.net>
 <563CF1A9.8030700@arm.com>
 <20151106111030.6cc5a032@icelake>
 <563D21E5.4050408@arm.com>
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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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