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From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Lukasz Majewski <l.majewski@samsung.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Jonghwa Lee <jonghwa3.lee@samsung.com>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux PM list <linux-pm@vger.kernel.org>,
	"cpufreq@vger.kernel.org" <cpufreq@vger.kernel.org>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	"sw0312.kim@samsung.com" <sw0312.kim@samsung.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [RFC PATCH 0/2] cpufreq: Introduce LAB cpufreq governor.
Date: Wed, 10 Apr 2013 11:14:01 +0100	[thread overview]
Message-ID: <20130410101400.GA4981@e102568-lin.cambridge.arm.com> (raw)
In-Reply-To: <20130410104452.661902af@amdc308.digital.local>

On Wed, Apr 10, 2013 at 09:44:52AM +0100, Lukasz Majewski wrote:

[...]

> > Have you also looked at the power clamp driver that have similar
> > target ?
> 
> I might be wrong here, but in my opinion the power clamp driver is a bit
> different:
> 
> 1. It is dedicated to Intel SoCs, which provide special set of
> registers (i.e. MSR_PKG_Cx_RESIDENCY [*]), which forces a processor to
> enter certain C state for a given duration. Idle duration is calculated
> by per CPU set of high priority kthreads (which also program [*]
> registers). 
> 

Those registers are used for compensation (ie user asked a given idle
ratio but HW stats show a mismatch) and they are not "programmed"
they are just read. That code is Intel specific but it can be easily ported
to ARM, I did that and most of the code is common with zero dependency
on the architecture.

> 2. ARM SoCs don't have such infrastructure, so we depend on SW here.

Well, it is true that most of the SoCs I am working on do not have
a programming interface to monitor C-state residency, granted, this is
a problem. If those stats can be retrieved somehow (I did that on our TC2
platform) then power clamp can be used on ARM with minor modifications.

Lorenzo


  parent reply	other threads:[~2013-04-10 10:14 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-01  8:24 [RFC PATCH 0/2] cpufreq: Introduce LAB cpufreq governor Jonghwa Lee
2013-04-01  8:24 ` [RFC PATCH 1/2] cpuidle: Add idle enter/exit time stamp for notifying current idle state Jonghwa Lee
2013-04-02  5:00   ` Daniel Lezcano
2013-04-02  5:00     ` Daniel Lezcano
2013-04-02  6:17     ` jonghwa3.lee
2013-04-02  7:34       ` Daniel Lezcano
2013-04-02  9:37         ` jonghwa3.lee
2013-04-02 10:08           ` Daniel Lezcano
2013-04-02 11:07             ` jonghwa3.lee
2013-04-02 11:18               ` Daniel Lezcano
2013-04-03  6:10                 ` jonghwa3.lee
2013-04-01  8:24 ` [RFC PATCH 2/2] cpufreq: Introduce new cpufreq governor, LAB(Legacy Application Boost) Jonghwa Lee
2013-04-01 15:37 ` [RFC PATCH 0/2] cpufreq: Introduce LAB cpufreq governor Viresh Kumar
2013-04-09 10:37   ` Lukasz Majewski
2013-04-09 12:02     ` Viresh Kumar
2013-04-09 16:44       ` Lukasz Majewski
     [not found]         ` <CAKfTPtD6MK9ogq7mOijSxLSsH0n65Xra48XfRSB3DFs35GT=2g@mail.gmail.com>
2013-04-10  6:56           ` Vincent Guittot
2013-04-10  8:44           ` Lukasz Majewski
2013-04-10  8:44             ` Lukasz Majewski
2013-04-10  9:13             ` Vincent Guittot
2013-04-10  9:38               ` Lukasz Majewski
2013-04-10 10:45                 ` Vincent Guittot
2013-04-23  7:28               ` Lukasz Majewski
2013-04-23  7:53                 ` Vincent Guittot
2013-04-10 10:14             ` Lorenzo Pieralisi [this message]
2013-04-09 12:25     ` jonghwa3.lee

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