linux-kernel - RE: [PATCH 0/4] CPUFreq: Implement per policy instances of governors

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Date:	Tue, 5 Feb 2013 11:29:04 +0000
From:	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Borislav Petkov <bp@...en8.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	Robin Randhawa <Robin.Randhawa@....com>,
	Steve Bannister <Steve.Bannister@....com>,
	Liviu Dudau <Liviu.Dudau@....com>
Subject: RE: [PATCH 0/4] CPUFreq: Implement per policy instances of governors

>
> Qualcomm's ARM based "krait". Currently shipping in millions of Android
> phones.
>
> http://en.wikipedia.org/wiki/Krait_(CPU)
>
> Thanks Charles for pointing it out, I knew there is one :)
>
> --
> viresh

> On 4 February 2013 19:06, Borislav Petkov <bp@...en8.de> wrote:
> > On Mon, Feb 04, 2013 at 06:55:25PM +0530, Viresh Kumar wrote:
>
> >> Its not only for multicluster system, but a system where multiple cpus
> >> have separate clock control and hence multiple policy structures.
> >
> > What are those systems? Examples?
>
> Qualcomm's ARM based "krait". Currently shipping in millions of Android
> phones.
>
> http://en.wikipedia.org/wiki/Krait_(CPU)
>
> Thanks Charles for pointing it out, I knew there is one :)
>
> --
> viresh

Actually shooting myself in the foot here, Krait is not such a great example because although you can use difference between frequencies you are less likely to use different tunables (not inconceivable but unlikely). The best examples systems are multi cluster and hereterogeneous systems, like the recently announced Samsung Exynos 5 octa http://en.wikipedia.org/wiki/Exynos_(system_on_chip). We will see more systems like this appearing, sporting low power cores combined with high performance ones, all running at the same time. I appreciate this is all very new, but more will come, and the requirement to have different tunables per cluster is very real. In ARM on our own multi cluster test chip, using an experimental version of this approach, we have seen good improvements in power consumption without compromising performance.

(Apologies ahead for any bit my mail server appends, not much I can do about it)

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