linux-kernel - Re: [PATCH v6 1/7] topology: Add a new arch_scale_freq

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Date:   Tue, 28 Nov 2023 16:00:03 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
        lukasz.luba@....com, pierre.gondois@....com,
        beata.michalska@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
        conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH v6 1/7] topology: Add a new arch_scale_freq_reference

On Tuesday 28 Nov 2023 at 15:52:52 (+0000), Ionela Voinescu wrote:
> Hi Vincent,
> 
> I have a small request on this patch, which is useful for [1].
> I'll detail what is needed lower in the code.
> 
> [1] https://lore.kernel.org/lkml/ZWYDr6JJJzBvsqf0@arm.com/
> 
> On Thursday 09 Nov 2023 at 11:14:32 (+0100), Vincent Guittot wrote:
> > @@ -279,13 +278,13 @@ void topology_normalize_cpu_scale(void)
> >  
> >  	capacity_scale = 1;
> >  	for_each_possible_cpu(cpu) {
> > -		capacity = raw_capacity[cpu] * per_cpu(freq_factor, cpu);
> > +		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
> 
> The only affected code that I could find is here and below.
> 
> The above line would have to change to:
> capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu) ?: 1;
> 
> >  		capacity_scale = max(capacity, capacity_scale);
> >  	}
> >  
> >  	pr_debug("cpu_capacity: capacity_scale=%llu\n", capacity_scale);
> >  	for_each_possible_cpu(cpu) {
> > -		capacity = raw_capacity[cpu] * per_cpu(freq_factor, cpu);
> > +		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
> 
> and here:
> capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu) ?: 1;
> 
> I think it's nicer to start with capacity_freq_ref as 0 and compensate here
> for uninitialized capacity_freq_ref.
> 
> Let me know if this is alright of if you'd prefer us to make this change
> in a separate patch.
> 
> Thanks,
> Ionela.
> 

Correction - both will need to be:
capacity = raw_capacity[cpu] * (per_cpu(capacity_freq_ref, cpu) ?: 1);

Thanks,
Ionela.