linux-kernel - Re: [PATCH v2 2/7] cpufreq: set invariance scale factor on transition end

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Message-ID: <20200805103452.GA4817@arm.com>
Date:   Wed, 5 Aug 2020 11:35:05 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     rjw@...ysocki.net, dietmar.eggemann@....com,
        catalin.marinas@....com, sudeep.holla@....com, will@...nel.org,
        linux@...linux.org.uk, mingo@...hat.com, peterz@...radead.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] cpufreq: set invariance scale factor on
 transition end

On Tuesday 04 Aug 2020 at 11:56:11 (+0530), Viresh Kumar wrote:
[..]
> > > >  - In __target_index(), cpufreq_freq_transition_end() is called only for
> > > >    drivers that have synchronous notifications enabled. There is only one
> > > >    driver that disables them,
> > > > 
> > > >    drivers/cpufreq/powernow-k8.c:1142: .flags = CPUFREQ_ASYNC_NOTIFICATION,
> > > > 
> > > >    which is deprecated.
> > > 
> > > I don't think this is deprecated.
> 
> Heh, maybe I misunderstood. I thought you are talking about the flag,
> while you were talking about the driver.
> 
> > Sorry, possibly 'deprecated' is a strong word.
> > 
> > As far as I knew acpi_cpufreq was recommended more recently for K8/K10
> > CPUs so that's why I decided not to create a special case for it, also
> > considering that it was not supporting cpufreq-based frequency
> > invariance to begin with.
> > 
> > We could support this as well by having a call to arch_set_freq_scale()
> > on the else path in __target_index(). But given that there was only this
> > one user of CPUFREQ_ASYNC_NOTIFICATION, I thought I'd propose this simpler
> > version first.
> > 
> > Let me know if my reasoning is wrong.
> 
> Nevertheless, I don't think you need to mention this detail in
> changelog for powernow-k8 as cpufreq_freq_transition_end() does get
> called for it as well, by the driver instead of the core.
> 

Agreed!

Many thanks,
Ionela.

> -- 
> viresh