linux-kernel - Re: [PATCH] sched: Take thermal pressure into account when determine rt fits capacity

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Date:   Tue, 10 May 2022 15:56:25 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Xuewen Yan <xuewen.yan94@...il.com>
Cc:     Xuewen Yan <xuewen.yan@...soc.com>, dietmar.eggemann@....com,
        lukasz.luba@....com, rafael@...nel.org, viresh.kumar@...aro.org,
        mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        rostedt@...dmis.org, linux-kernel@...r.kernel.org,
        di.shen@...soc.com
Subject: Re: [PATCH] sched: Take thermal pressure into account when determine
 rt fits capacity

Hi Xuewen

On 05/09/22 10:29, Xuewen Yan wrote:

[...]

> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a68482d66535..44c7c2598d87 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8399,16 +8399,37 @@ static unsigned long scale_rt_capacity(int cpu)
> >
> >  static void update_cpu_capacity(struct sched_domain *sd, int cpu)
> >  {
> > +       unsigned long capacity_orig = arch_scale_cpu_capacity(cpu);
> >         unsigned long capacity = scale_rt_capacity(cpu);
> >         struct sched_group *sdg = sd->groups;
> > +       struct rq *rq = cpu_rq(cpu);
> >
> > -       cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu);
> > +       rq->cpu_capacity_orig = capacity_orig;
> >
> >         if (!capacity)
> >                 capacity = 1;
> >
> > -       cpu_rq(cpu)->cpu_capacity = capacity;
> > -       trace_sched_cpu_capacity_tp(cpu_rq(cpu));
> > +       rq->cpu_capacity = capacity;
> > +       trace_sched_cpu_capacity_tp(rq);
> > +
> > +       if (static_branch_unlikely(&sched_asym_cpucapacity)) {
> > +               unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);
> 
> Indeed, I prefer arch_thermal_pressure here, because the
> thermal_load_avg would change over time,
> but the inv_cap's update period may could not keep up with his changes.

If that's what works for you, I think that's fine. Vincent, Lukasz you okay
with that?

> 
> > +
> > +               rq->cpu_capacity_inverted = 0;
> > +
> > +               for_each_possible_cpu(cpu) {
> > +                       unsigned long cap = arch_scale_cpu_capacity(cpu);
> > +
> > +                       if (capacity_orig <= cap)
> > +                               continue;
> > +
> > +                       if (cap > inv_cap) {
> > +                               rq->cpu_capacity_inverted = inv_cap;
> > +                               break;
> > +                       }
> > +               }
> > +
> > +       }
> >
> >         sdg->sgc->capacity = capacity;
> >         sdg->sgc->min_capacity = capacity;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 8dccb34eb190..bfe84c870bf9 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -992,6 +992,7 @@ struct rq {
> >
> >         unsigned long           cpu_capacity;
> >         unsigned long           cpu_capacity_orig;
> > +       unsigned long           cpu_capacity_inverted;
> >
> >         struct callback_head    *balance_callback;
> >
> > @@ -2807,6 +2808,11 @@ static inline unsigned long capacity_orig_of(int cpu)
> >         return cpu_rq(cpu)->cpu_capacity_orig;
> >  }
> >
> > +static inline unsigned long cpu_in_capacity_inversion(int cpu)
> > +{
> > +       return cpu_rq(cpu)->cpu_capacity_inverted;
> > +}
> > +
> >  /**
> >   * enum cpu_util_type - CPU utilization type
> >   * @FREQUENCY_UTIL:    Utilization used to select frequency
> >
> >
> > --->8---
> 
> The patch is amazing for me, and the complexity is not too high. Would
> you please push the patch?
> I think the idea is yours, I don't want to use it as my patch v2.

I'd be happy to add a commit message so that you can include it in your v2.

First, I'd like to hear from Vincent and Lukasz they're happy with this
approach.

I've been trying to think how we can do this generically but can't find an
alternative to the extra loop or additional fallback_cpu_mask. Maybe the mask
is okay if we protect it with sched_asymmetric_cpucapacity static key..

Thanks

--
Qais Yousef