linux-kernel - R: R: [RFC PATCH v3 0/2] Add Krait Cache Scaling support

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Message-ID: <01f201d681e1$70ff1bc0$52fd5340$@gmail.com>
Date:   Thu, 3 Sep 2020 13:00:27 +0200
From:   <ansuelsmth@...il.com>
To:     "'Sibi Sankar'" <sibis@...eaurora.org>,
        "'Viresh Kumar'" <viresh.kumar@...aro.org>
Cc:     <vincent.guittot@...aro.org>, <saravanak@...gle.com>,
        "'Sudeep Holla'" <sudeep.holla@....com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        "'Rob Herring'" <robh+dt@...nel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: R: R: [RFC PATCH v3 0/2] Add Krait Cache Scaling support



> -----Messaggio originale-----
> Da: sibis=codeaurora.org@...codeaurora.org
> <sibis=codeaurora.org@...codeaurora.org> Per conto di Sibi Sankar
> Inviato: giovedì 3 settembre 2020 09:13
> A: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: ansuelsmth@...il.com; vincent.guittot@...aro.org;
> saravanak@...gle.com; 'Sudeep Holla' <sudeep.holla@....com>; 'Rafael J.
> Wysocki' <rjw@...ysocki.net>; 'Rob Herring' <robh+dt@...nel.org>; linux-
> pm@...r.kernel.org; devicetree@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Oggetto: Re: R: [RFC PATCH v3 0/2] Add Krait Cache Scaling support
> 
> On 2020-09-03 12:23, Viresh Kumar wrote:
> > On 31-08-20, 09:41, ansuelsmth@...il.com wrote:
> >> On 31-08-20, Sibi wrote:
> >> > On 2020-08-24 16:10, Viresh Kumar wrote:
> >> > > +Vincent/Saravana/Sibi
> >> > >
> >> > > On 21-08-20, 16:00, Ansuel Smith wrote:
> >> > >> This adds Krait Cache scaling support using the cpufreq notifier.
> >> > >> I have some doubt about where this should be actually placed (clk
> or
> >> > >> cpufreq)?
> >> > >> Also the original idea was to create a dedicated cpufreq driver
(like
> >> > >> it's done in
> >> > >> the codeaurora qcom repo) by copying the cpufreq-dt driver and
> adding
> >> > >> the cache
> >> > >> scaling logic but i still don't know what is better. Have a very
> >> > >> similar driver or
> >> > >> add a dedicated driver only for the cache using the cpufreq
notifier
> >> > >> and do the
> >> > >> scale on every freq transition.
> >> > >> Thanks to everyone who will review or answer these questions.
> >> > >
> >> > > Saravana was doing something with devfreq to solve such issues if I
> >> > > wasn't mistaken.
> >> > >
> >> > > Sibi ?
> >> >
> >> > IIRC the final plan was to create a devfreq device
> >> > and devfreq-cpufreq based governor to scale them, this
> >> > way one can switch to a different governor if required.
> >>
> >> So in this case I should convert this patch to a devfreq driver-
> >
> > I think this should happen nevertheless. You are doing DVFS for a
> > device which isn't a CPU and devfreq looks to be the right place of
> > doing so.
> >
> >> Isn't overkill to use a governor for such a task?
> >> (3 range based on the cpufreq?)
> >
> > I am not sure about the governor part here, maybe it won't be required
> > ?
> 
> Yeah I don't see it being needed in ^^
> case as well. I just mentioned them as
> an advantage in case you wanted to switch
> to a different governor in the future.
> 
> https://lore.kernel.org/lkml/d0bc8877-6d41-f54e-1c4c-
> 2fadbb9dcd0b@...sung.com/
> 
> A devfreq governor tracking cpufreq was
> generally accepted but using a cpufreq
> notifier to achieve that was discouraged.
> 

I read the patch discussion and it looks like at the very end they
lost interest in pushing it. That would very fit what I need here so
I'm asking how should I proceed? Keep the cpufreq notifier?
Introduce a dedicated governor? Ask them to resume the pushing or
try to include the changes to the passive governor by myself? 

> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project.