linux-kernel - Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection framework

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Date:   Wed, 13 Jun 2018 20:32:50 +0000
From:   "Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:     "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "edubezval@...il.com" <edubezval@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "andrea.parri@...rulasolutions.com" 
        <andrea.parri@...rulasolutions.com>,
        "kevin.wangtao@...aro.org" <kevin.wangtao@...aro.org>,
        "leo.yan@...aro.org" <leo.yan@...aro.org>,
        "daniel.thompson@...aro.org" <daniel.thompson@...aro.org>,
        "javi.merino@...nel.org" <javi.merino@...nel.org>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>
Subject: Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle
 injection framework

On Wed, 2018-06-13 at 22:19 +0200, Daniel Lezcano wrote:
> On 13/06/2018 22:07, Pandruvada, Srinivas wrote:
> > On Wed, 2018-06-13 at 22:00 +0200, Daniel Lezcano wrote:
> > > On 13/06/2018 17:54, Pandruvada, Srinivas wrote:
> > > > On Tue, 2018-06-12 at 14:00 +0200, Daniel Lezcano wrote:
> > > > > Initially, the cpu_cooling device for ARM was changed by
> > > > > adding a
> > > > > new
> > > > > policy inserting idle cycles. The intel_powerclamp driver
> > > > > does a
> > > > > similar action.
> > > > > 
> > > > > Instead of implementing idle injections privately in the
> > > > > cpu_cooling
> > > > > device, move the idle injection code in a dedicated framework
> > > > > and
> > > > > give
> > > > > the opportunity to other frameworks to make use of it.
> > > > > 
> > > > > The framework relies on the smpboot kthreads which handles
> > > > > via
> > > > > its
> > > > > main loop the common code for hotplugging and [un]parking.
> > > > > 
> > > > > This code was previously tested with the cpu cooling device
> > > > > and
> > > > > went
> > > > > through several iterations. It results now in split code and
> > > > > API
> > > > > exported in the header file. It was tested with the cpu
> > > > > cooling
> > > > > device
> > > > > with success.
> > > > > 
> > > > 
> > > > May be I have missed, but I don't see any use of powercap
> > > > sysfs.
> > > > 
> > > > We created powercap sys that user space is presented a common
> > > > interface
> > > > for power capping. The RAPL driver was also submitted as
> > > > cooling
> > > > device
> > > > before, but suggestion was to create this powercap.
> > > > 
> > > > So if powercap interface is not enough then may be we should
> > > > enhance
> > > > that.
> > > 
> > > We are creating a framework for idle injection. This framework
> > > can
> > > then
> > > be used by the cpu_cooling device, the power_clamp and in
> > > addition a
> > > power capping for ARM (if it makes sense).
> > 
> > But in this case, why in drivers/powercap folder as this is another
> > framework?
> 
> I presented at OSPM 2nd the cpu idle cooling device. It is ARM
> specific
> but has some similarities with the power clamp driver.
> 
> Some board come with power numbers defined in their DT and from there
> we
> are able to compute a targeted power by injecting idle cycles.
> 
> As the idle injection allows to do also power capping, Rafael told me
> to
> move that to a framework (may be better say a component with exported
> services or library) and put it in drivers/powercap.
So Rafael wants it to be in powercap.

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