linux-kernel - Re: [PATCH] sched: cpufreq: Rename map_util_perf to apply_dvfs

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Message-ID: <20240220135828.t4dhy5tmfrsrzn6y@airbuntu>
Date: Tue, 20 Feb 2024 13:58:28 +0000
From: Qais Yousef <qyousef@...alina.io>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] sched: cpufreq: Rename map_util_perf to
 apply_dvfs_headroom

On 02/12/24 16:54, Rafael J. Wysocki wrote:
> On Mon, Feb 5, 2024 at 3:20 AM Qais Yousef <qyousef@...alina.io> wrote:
> >
> > We are providing headroom for the utilization to grow until the next
> > decision point to pick the next frequency. Give the function a better
> > name and give it some documentation. It is not really mapping anything.
> >
> > Also move it to sched.h. This function relies on updating util signal
> > appropriately to give a headroom to grow. This is more of a scheduler
> > functionality than cpufreq. Move it to sched.h where all the other util
> > handling code belongs.
> >
> > Signed-off-by: Qais Yousef <qyousef@...alina.io>
> > ---
> >  include/linux/sched/cpufreq.h    |  5 -----
> >  kernel/sched/cpufreq_schedutil.c |  2 +-
> >  kernel/sched/sched.h             | 17 +++++++++++++++++
> >  3 files changed, 18 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> > index bdd31ab93bc5..d01755d3142f 100644
> > --- a/include/linux/sched/cpufreq.h
> > +++ b/include/linux/sched/cpufreq.h
> > @@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
> >  {
> >         return freq * util / cap;
> >  }
> > -
> > -static inline unsigned long map_util_perf(unsigned long util)
> > -{
> > -       return util + (util >> 2);
> > -}
> >  #endif /* CONFIG_CPU_FREQ */
> >
> >  #endif /* _LINUX_SCHED_CPUFREQ_H */
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 95c3c097083e..abbd1ddb0359 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -179,7 +179,7 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> >                                  unsigned long max)
> >  {
> >         /* Add dvfs headroom to actual utilization */
> > -       actual = map_util_perf(actual);
> > +       actual = apply_dvfs_headroom(actual);
> >         /* Actually we don't need to target the max performance */
> >         if (actual < max)
> >                 max = actual;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index e58a54bda77d..0da3425200b1 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -3002,6 +3002,23 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> >                                  unsigned long min,
> >                                  unsigned long max);
> >
> > +/*
> > + * DVFS decision are made at discrete points. If CPU stays busy, the util will
> > + * continue to grow, which means it could need to run at a higher frequency
> > + * before the next decision point was reached. IOW, we can't follow the util as
> > + * it grows immediately, but there's a delay before we issue a request to go to
> > + * higher frequency. The headroom caters for this delay so the system continues
> > + * to run at adequate performance point.
> > + *
> > + * This function provides enough headroom to provide adequate performance
> > + * assuming the CPU continues to be busy.
> > + *
> > + * At the moment it is a constant multiplication with 1.25.
> > + */
> > +static inline unsigned long apply_dvfs_headroom(unsigned long util)
> > +{
> > +       return util + (util >> 2);
> > +}
> >
> >  /*
> >   * Verify the fitness of task @p to run on @cpu taking into account the
> > --
> 
> This touches sched.h, so I'd prefer it to go in via tip and
> 
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>

Thanks