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Subject: Re: [RFC v3 6/6] arm64/amu: use capacity_ref_freq to set AMU ratio

On Thu, 26 Oct 2023 at 13:19, Dietmar Eggemann <[email protected]> wrote:
>
> On 24/10/2023 11:58, Vincent Guittot wrote:
> > On Mon, 23 Oct 2023 at 22:58, Ionela Voinescu <[email protected]> wrote:
> >>
> >> Hi,
> >>
> >> On Wednesday 18 Oct 2023 at 18:25:40 (+0200), Vincent Guittot wrote:
> >>> Use the new capacity_ref_freq to set the ratio that is used by AMU for
> >>> computing the arch_scale_freq_capacity().
> >>> This helps to keep everything aligned using the same reference for
> >>> computing CPUs capacity.
> >>>
> >>> The default value of the ratio ensures that arch_scale_freq_capacity()
> >>> returns max capacity until it is set to its correct value with the
> >>> cpu capacity and capacity_ref_freq.
>
> Nitpick: Could you mention that arch_max_freq_scale is the default value
> for this ratio? Took me a while to recreate the (not so simple) story
> for this change, i.e. make the connection between ratio and
> arch_max_freq_scale.

something like :
"
The default value of the ratio (saved in per_cpu(arch_max_freq_scale)
ensures that arch_scale_freq_capacity() returns max capacity until it
is set to its correct value with the cpu capacity and
capacity_ref_freq.
"

Or I can rename the variable per_cpu(arch_max_freq_ratio)

>
> init_cpu_capacity_callback()
>
> freq_inv_set_max_ratio()
>
> u64 ratio
> ...
> per_cpu(arch_max_freq_scale, cpu) = (unsigned long)ratio
> ^^^^^^^^^^^^^^^^^^^
>
>
> static struct scale_freq_data amu_sfd = {
> .set_freq_scale = amu_scale_freq_tick,
> }
>
> #define arch_scale_freq_tick topology_scale_freq_tick
>
> topology_scale_freq_tick()
>
> sfd->set_freq_scale()
>
>
> amu_scale_freq_tick()
>
> ...
> scale *= this_cpu_read(arch_max_freq_scale)
> ^^^^^^^^^^^^^^^^^^^
> ...
> this_cpu_write(arch_freq_scale, (unsigned long)scale);
>
>
> #define arch_scale_freq_capacity topology_get_freq_scale
>
> topology_get_freq_scale(cpu)
>
> return per_cpu(arch_freq_scale, cpu)
>
> [...]
>

2023-10-26 15:14:29

by Vincent Guittot

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Subject: Re: [PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

On Wed, 25 Oct 2023 at 22:13, Dietmar Eggemann <[email protected]> wrote:
>
> On 18/10/2023 18:25, Vincent Guittot wrote:
> > cpuinfo.max_freq can change at runtime because of boost as an example. This
> > implies that the value could be different than the one that has been
> > used when computing the capacity of a CPU.
> >
> > The new arch_scale_freq_ref() returns a fixed and coherent reference
> > frequency that can be used when computing a frequency based on utilization.
> >
> > Use this arch_scale_freq_ref() when available and fallback to
> > policy otherwise.
> >
> > Signed-off-by: Vincent Guittot <[email protected]>
> > Reviewed-by: Lukasz Luba <[email protected]>
> > Tested-by: Lukasz Luba <[email protected]>
> >
> > ---
> > kernel/sched/cpufreq_schedutil.c | 26 ++++++++++++++++++++++++--
> > 1 file changed, 24 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 458d359f5991..6e4030482ae8 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -114,6 +114,28 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
> > }
> > }
> >
> > +/**
> > + * cpufreq_get_capacity_ref_freq - get the reference frequency of a given CPU that
>
> s/cpufreq_get_capacity_ref_freq/get_capacity_ref_freq
>
> s/of a given CPU/for a given cpufreq policy ? (of which the CPU managing
> it is used for the arch_scale_freq_ref() call in the function.
>
> > + * has been used to correlate frequency and compute capacity.
> > + * @policy: the cpufreq policy of the CPU in question.
> > + * @use_current: Fallback to current freq instead of policy->cpuinfo.max_freq.
>
> Looks like use_current does not exists as a parameter.

Thanks for the review. I'm going to apply your comments

>
> > + *
> > + * Return: the reference CPU frequency to compute a capacity.
> > + */
> > +static __always_inline
> > +unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
> > +{
> > + unsigned int freq = arch_scale_freq_ref(policy->cpu);
> > +
> > + if (freq)
> > + return freq;
> > +
> > + if (arch_scale_freq_invariant())
> > + return policy->cpuinfo.max_freq;
> > +
> > + return policy->cur;
> > +}
>
> Reviewed-by: Dietmar Eggemann <[email protected]>
>
>
>