linux-kernel - Re: [PATCH v4 6/7] arm64: use activity monitors for frequency invariance

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Message-ID: <20200226101847.GA19513@arm.com>
Date:   Wed, 26 Feb 2020 10:18:47 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        maz@...nel.org, suzuki.poulose@....com, sudeep.holla@....com,
        dietmar.eggemann@....com, rjw@...ysocki.net, peterz@...radead.org,
        mingo@...hat.com, vincent.guittot@...aro.org,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v4 6/7] arm64: use activity monitors for frequency
 invariance

Hi Valentin, Lukasz,

On Tuesday 25 Feb 2020 at 09:59:20 (+0000), Lukasz Luba wrote:
[..]
> On 2/24/20 6:40 PM, Valentin Schneider wrote:
> > 
> > Ionela Voinescu writes:
> > > +static inline int
> > 
> > That should be bool, seeing what it returns.
> > 

Will do!

[..]
> > > 
> > > +#ifndef arch_cpu_freq_counters
> > > +static __always_inline
> > > +bool arch_cpu_freq_counters(struct cpumask *cpus)
> > > +{
> > > +	return false;
> > > +}
> > > +#endif
> > > 
> > 
> > Apologies for commenting on this only now, I had missed it in my earlier
> > round of review.
> > 
> > I would've liked to keep this contained within arm64 stuff until we agreed
> > on a more generic counter-driven FIE interface, but seems like we can't evade
> > it due to the arch_topology situation.
> > 
> > Would it make sense to relocate this stub to arch_topology.h instead, at
> > least for the time being? That way the only non-arm64 changes are condensed
> > in arch_topology (even if it doesn't change much in terms of header files,
> > since topology.h imports arch_topology.h)
> 
> Or make it as a 'weak' and place it just above the arch_set_freq_scale()
> in arch_topology.c, not touching headers?

Yes, you guys are right, this works better nicely confined to
arch_topology.c/h. As Lukasz suggested, I'll make
arch_cpu_freq_counters (while here, it probably works better renamed to
arch_freq_counters_available) a weak function in arch_topology.c with
its strong definition in arm64/kernel/topology.c.

The diff is large(ish) so I'll push v5 directly with this change.

Thank you both for the review,
Ionela.