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Date: Tue, 10 Aug 2021 10:35:21 +0100 From: Lukasz Luba <lukasz.luba@....com> To: Viresh Kumar <viresh.kumar@...aro.org> 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 8/10/21 10:27 AM, Viresh Kumar wrote: > 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 It's good that it's just for fun ;) > (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. The EM is directly used by scheduler in the hot-path, there are no checks even if the EM if for CPUs. We are sure it's is for CPUs and is always there for all CPUs. I'm currently working on a EM v2 which would have stronger mechanisms and do better job in this field. The patches are under internal review and hopefully ready to post by the end of month. > > Again, since the routine is there already, I think it is better/fine > to just use it. True, it doesn't harm, so I commented it in the patch 1/8 that it could stay. > >>> 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. >
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