linux-kernel - Re: [PATCH 0/8] cpufreq: Auto-register with energy model

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Date:   Tue, 10 Aug 2021 14:57:05 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Andy Gross <agross@...nel.org>, Rafael Wysocki <rjw@...ysocki.net>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Fabio Estevam <festevam@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH 0/8] cpufreq: Auto-register with energy model

On 10-08-21, 10:17, Lukasz Luba wrote:
> Hi Viresh,
> 
> I like the idea, only small comments here in the cover letter.
> 
> On 8/10/21 8:36 AM, Viresh Kumar wrote:
> > Provide a cpufreq driver flag so drivers can ask the cpufreq core to register
> > with the EM core on their behalf. This allows us to get rid of duplicated code
> > in the drivers and fix the unregistration part as well, which none of the
> > drivers have done until now.
> 
> The EM is never freed for CPUs by design. The unregister function was
> introduced for devfreq devices.

I see. So if a cpufreq driver unregisters and registers again, it will
be required to use the entries created by the registration itself,
right ? Technically speaking, it is better to unregister and free any
related resources and parse everything again.

Lets say, just for fun, I want to test two copies of a cpufreq driver
(providing different set of freq-tables). I build both of them as
modules, insert the first version, remove it, insert the second one.
Ideally, this should just work as expected. But I don't think it will
in this case as you never parse the EM stuff again.

Again, since the routine is there already, I think it is better/fine
to just use it.

> > This would also make the registration with EM core to happen only after policy
> > is fully initialized, and the EM core can do other stuff from in there, like
> > marking frequencies as inefficient (WIP). Though this patchset is useful without
> > that work being done and should be merged nevertheless.
> > 
> > This doesn't update scmi cpufreq driver for now as it is a special case and need
> > to be handled differently. Though we can make it work with this if required.
> 
> The scmi cpufreq driver uses direct EM API, which provides flexibility
> and should stay as is.

Right, so I left it as is for now.

-- 
viresh