Date:   Mon, 30 Jan 2023 19:30:28 +0000
From:   Qais Yousef <qyousef@layalina.io>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     mingo@kernel.org, peterz@infradead.org, dietmar.eggemann@arm.com,
        rafael@kernel.org, viresh.kumar@linaro.org, vschneid@redhat.com,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        lukasz.luba@arm.com, wvw@google.com, xuewen.yan94@gmail.com,
        han.lin@mediatek.com, Jonathan.JMChen@mediatek.com
Subject: Re: [PATCH v4] sched/fair: unlink misfit task from cpu overutilized
Message-ID: <20230130193028.pkzq5wwxb5ivfwnn@airbuntu>
References: <20230119174244.2059628-1-vincent.guittot@linaro.org>
 <20230129163538.mxkr5ib2glqu36ww@airbuntu>
 <CAKfTPtADvhtXGn71P_1LoHDm=soUZu3Qi9ziAGfQE9Ob-cs-CA@mail.gmail.com>
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On 01/30/23 15:13, Vincent Guittot wrote:
> On Sun, 29 Jan 2023 at 17:35, Qais Yousef <qyousef@layalina.io> wrote:
> >
> > On 01/19/23 18:42, Vincent Guittot wrote:
> > > By taking into account uclamp_min, the 1:1 relation between task misfit
> > > and cpu overutilized is no more true as a task with a small util_avg may
> > > not fit a high capacity cpu because of uclamp_min constraint.
> > >
> > > Add a new state in util_fits_cpu() to reflect the case that task would fit
> > > a CPU except for the uclamp_min hint which is a performance requirement.
> > >
> > > Use -1 to reflect that a CPU doesn't fit only because of uclamp_min so we
> > > can use this new value to take additional action to select the best CPU
> > > that doesn't match uclamp_min hint.
> > >
> > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > > ---
> >
> > I did improve my unit test so that I look at overutilized and misfit condition.
> >
> > Of course I had to hack the kernel to expose something to manipulate the
> > thermal pressure signal. I also made sure to use the sched_energy_aware knob to
> > switch between using EAS/CAS so that both feec() and sic() are exercised.
> >
> > My test system is pinebook pro which has a simple 2 level capacities - but
> > I couldn't catch anything wrong. Only one unrelated failure - see below.
> >
> > I'd be happy to give this my Reviewed-and-tested-by. What's the plan for the
> > removal the capacity_inversion logic?
> 
> Thanks for the  Reviewed-and-tested-by.
> 
> Regarding the removal of capacity_inversion logic , I don't know how
> Peter prefers to handle this in one step with this patch then the
> reverts or revert capacity_inversion logic in a 2nd step

Or just fold the removal into this patch?

I think your patch should at least include this part

	diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
	index dcbcb496b879..27cc5a029c22 100644
	--- a/kernel/sched/fair.c
	+++ b/kernel/sched/fair.c
	@@ -4476,17 +4476,9 @@ static inline int util_fits_cpu(unsigned long util,
		 *
		 * For uclamp_max, we can tolerate a drop in performance level as the
		 * goal is to cap the task. So it's okay if it's getting less.
	-        *
	-        * In case of capacity inversion we should honour the inverted capacity
	-        * for both uclamp_min and uclamp_max all the time.
		 */
	-       capacity_orig = cpu_in_capacity_inversion(cpu);
	-       if (capacity_orig) {
	-               capacity_orig_thermal = capacity_orig;
	-       } else {
	-               capacity_orig = capacity_orig_of(cpu);
	-               capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
	-       }
	+       capacity_orig = capacity_orig_of(cpu);
	+       capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);

		/*
		 * We want to force a task to fit a cpu as implied by uclamp_max.

but the rest is not a lot of code to remove luckily, so doing it all in one go
might be easier.


Cheers

--
Qais Yousef

> 
> >
> > And nit: subject line could still be improved :) This is a lot more than
> > unlinking misfit from OU.
> >
> > >
> > > Change since v3:
> > > - Keep current condition for uclamp_max_fits in util_fits_cpu()
> > > - Update some comments
> > >
> > >  kernel/sched/fair.c | 105 ++++++++++++++++++++++++++++++++++----------
> > >  1 file changed, 82 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index d4db72f8f84e..54e14da53274 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -4561,8 +4561,8 @@ static inline int util_fits_cpu(unsigned long util,
> > >        * handle the case uclamp_min > uclamp_max.
> > >        */
> > >       uclamp_min = min(uclamp_min, uclamp_max);
> > > -     if (util < uclamp_min && capacity_orig != SCHED_CAPACITY_SCALE)
> > > -             fits = fits && (uclamp_min <= capacity_orig_thermal);
> > > +     if (fits && (util < uclamp_min) && (uclamp_min > capacity_orig_thermal))
> > > +             return -1;
> > >
> > >       return fits;
> > >  }
> > > @@ -4572,7 +4572,11 @@ static inline int task_fits_cpu(struct task_struct *p, int cpu)
> > >       unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN);
> > >       unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX);
> > >       unsigned long util = task_util_est(p);
> > > -     return util_fits_cpu(util, uclamp_min, uclamp_max, cpu);
> > > +     /*
> > > +      * Return true only if the cpu fully fits the task requirements, which
> > > +      * include the utilization but also the performance hints.
> > > +      */
> > > +     return (util_fits_cpu(util, uclamp_min, uclamp_max, cpu) > 0);
> > >  }
> > >
> > >  static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> > > @@ -6138,6 +6142,7 @@ static inline bool cpu_overutilized(int cpu)
> > >       unsigned long rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN);
> > >       unsigned long rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX);
> > >
> > > +     /* Return true only if the utilization doesn't fits CPU's capacity */
> > >       return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu);
> > >  }
> > >
> > > @@ -6931,6 +6936,7 @@ static int
> > >  select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
> > >  {
> > >       unsigned long task_util, util_min, util_max, best_cap = 0;
> > > +     int fits, best_fits = 0;
> > >       int cpu, best_cpu = -1;
> > >       struct cpumask *cpus;
> > >
> > > @@ -6946,12 +6952,28 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
> > >
> > >               if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu))
> > >                       continue;
> > > -             if (util_fits_cpu(task_util, util_min, util_max, cpu))
> > > +
> > > +             fits = util_fits_cpu(task_util, util_min, util_max, cpu);
> > > +
> > > +             /* This CPU fits with all requirements */
> > > +             if (fits > 0)
> > >                       return cpu;
> > > +             /*
> > > +              * Only the min performance hint (i.e. uclamp_min) doesn't fit.
> > > +              * Look for the CPU with best capacity.
> > > +              */
> > > +             else if (fits < 0)
> > > +                     cpu_cap = capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu));
> > >
> > > -             if (cpu_cap > best_cap) {
> > > +             /*
> > > +              * First, select CPU which fits better (-1 being better than 0).
> > > +              * Then, select the one with best capacity at same level.
> > > +              */
> > > +             if ((fits < best_fits) ||
> > > +                 ((fits == best_fits) && (cpu_cap > best_cap))) {
> > >                       best_cap = cpu_cap;
> > >                       best_cpu = cpu;
> > > +                     best_fits = fits;
> > >               }
> > >       }
> >
> > Not something you introduced, but I had a 'failure' case when I ran a task with
> > (uclamp_min, uclamp_max) = (1024, 1024) followed by (0, 0) in CAS.
> >
> > The task was basically stuck on big core and I check if the task can run on the
> > smallest possible capacity in my test.
> >
> > This is a separate problem that we should address out of this patch. One can
> > argue CAS is not energy aware, so any fitting cpu is okay. But one of the goals
> > of uclamp_max is to help keep some busy tasks away from bigger cores when
> > possible - not only for power reasons, but also for perf reasons as they can
> > 'steal' resources from other tasks. So the lack of a more comprehensive search
> > is a weakness and something we can improve on.
> >
> > feec() behaves fine - but after applying some fixes that I've been sleeping on
> > for a bit. Should see them in your inbox now.
> >
> > Thanks for the patch! I am still wary of the complexity, but the fallback
> > search could lead to better placement results now.
> >
> >
> > Cheers
> >
> > --
> > Qais Yousef
> >
> > >
> > > @@ -6964,7 +6986,11 @@ static inline bool asym_fits_cpu(unsigned long util,
> > >                                int cpu)
> > >  {
> > >       if (sched_asym_cpucap_active())
> > > -             return util_fits_cpu(util, util_min, util_max, cpu);
> > > +             /*
> > > +              * Return true only if the cpu fully fits the task requirements
> > > +              * which include the utilization and the performance hints.
> > > +              */
> > > +             return (util_fits_cpu(util, util_min, util_max, cpu) > 0);
> > >
> > >       return true;
> > >  }
> > > @@ -7331,6 +7357,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >       unsigned long p_util_max = uclamp_is_used() ? uclamp_eff_value(p, UCLAMP_MAX) : 1024;
> > >       struct root_domain *rd = this_rq()->rd;
> > >       int cpu, best_energy_cpu, target = -1;
> > > +     int prev_fits = -1, best_fits = -1;
> > > +     unsigned long best_thermal_cap = 0;
> > > +     unsigned long prev_thermal_cap = 0;
> > >       struct sched_domain *sd;
> > >       struct perf_domain *pd;
> > >       struct energy_env eenv;
> > > @@ -7366,6 +7395,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >               unsigned long prev_spare_cap = 0;
> > >               int max_spare_cap_cpu = -1;
> > >               unsigned long base_energy;
> > > +             int fits, max_fits = -1;
> > >
> > >               cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
> > >
> > > @@ -7418,7 +7448,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >                                       util_max = max(rq_util_max, p_util_max);
> > >                               }
> > >                       }
> > > -                     if (!util_fits_cpu(util, util_min, util_max, cpu))
> > > +
> > > +                     fits = util_fits_cpu(util, util_min, util_max, cpu);
> > > +                     if (!fits)
> > >                               continue;
> > >
> > >                       lsub_positive(&cpu_cap, util);
> > > @@ -7426,7 +7458,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >                       if (cpu == prev_cpu) {
> > >                               /* Always use prev_cpu as a candidate. */
> > >                               prev_spare_cap = cpu_cap;
> > > -                     } else if (cpu_cap > max_spare_cap) {
> > > +                             prev_fits = fits;
> > > +                     } else if ((fits > max_fits) ||
> > > +                                ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
> > >                               /*
> > >                                * Find the CPU with the maximum spare capacity
> > >                                * among the remaining CPUs in the performance
> > > @@ -7434,6 +7468,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >                                */
> > >                               max_spare_cap = cpu_cap;
> > >                               max_spare_cap_cpu = cpu;
> > > +                             max_fits = fits;
> > >                       }
> > >               }
> > >
> > > @@ -7452,26 +7487,50 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > >                       if (prev_delta < base_energy)
> > >                               goto unlock;
> > >                       prev_delta -= base_energy;
> > > +                     prev_thermal_cap = cpu_thermal_cap;
> > >                       best_delta = min(best_delta, prev_delta);
> > >               }
> > >
> > >               /* Evaluate the energy impact of using max_spare_cap_cpu. */
> > >               if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
> > > +                     /* Current best energy cpu fits better */
> > > +                     if (max_fits < best_fits)
> > > +                             continue;
> > > +
> > > +                     /*
> > > +                      * Both don't fit performance hint (i.e. uclamp_min)
> > > +                      * but best energy cpu has better capacity.
> > > +                      */
> > > +                     if ((max_fits < 0) &&
> > > +                         (cpu_thermal_cap <= best_thermal_cap))
> > > +                             continue;
> > > +
> > >                       cur_delta = compute_energy(&eenv, pd, cpus, p,
> > >                                                  max_spare_cap_cpu);
> > >                       /* CPU utilization has changed */
> > >                       if (cur_delta < base_energy)
> > >                               goto unlock;
> > >                       cur_delta -= base_energy;
> > > -                     if (cur_delta < best_delta) {
> > > -                             best_delta = cur_delta;
> > > -                             best_energy_cpu = max_spare_cap_cpu;
> > > -                     }
> > > +
> > > +                     /*
> > > +                      * Both fit for the task but best energy cpu has lower
> > > +                      * energy impact.
> > > +                      */
> > > +                     if ((max_fits > 0) && (best_fits > 0) &&
> > > +                         (cur_delta >= best_delta))
> > > +                             continue;
> > > +
> > > +                     best_delta = cur_delta;
> > > +                     best_energy_cpu = max_spare_cap_cpu;
> > > +                     best_fits = max_fits;
> > > +                     best_thermal_cap = cpu_thermal_cap;
> > >               }
> > >       }
> > >       rcu_read_unlock();
> > >
> > > -     if (best_delta < prev_delta)
> > > +     if ((best_fits > prev_fits) ||
> > > +         ((best_fits > 0) && (best_delta < prev_delta)) ||
> > > +         ((best_fits < 0) && (best_thermal_cap > prev_thermal_cap)))
> > >               target = best_energy_cpu;
> > >
> > >       return target;
> > > @@ -10265,24 +10324,23 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> > >        */
> > >       update_sd_lb_stats(env, &sds);
> > >
> > > -     if (sched_energy_enabled()) {
> > > -             struct root_domain *rd = env->dst_rq->rd;
> > > -
> > > -             if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
> > > -                     goto out_balanced;
> > > -     }
> > > -
> > > -     local = &sds.local_stat;
> > > -     busiest = &sds.busiest_stat;
> > > -
> > >       /* There is no busy sibling group to pull tasks from */
> > >       if (!sds.busiest)
> > >               goto out_balanced;
> > >
> > > +     busiest = &sds.busiest_stat;
> > > +
> > >       /* Misfit tasks should be dealt with regardless of the avg load */
> > >       if (busiest->group_type == group_misfit_task)
> > >               goto force_balance;
> > >
> > > +     if (sched_energy_enabled()) {
> > > +             struct root_domain *rd = env->dst_rq->rd;
> > > +
> > > +             if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
> > > +                     goto out_balanced;
> > > +     }
> > > +
> > >       /* ASYM feature bypasses nice load balance check */
> > >       if (busiest->group_type == group_asym_packing)
> > >               goto force_balance;
> > > @@ -10295,6 +10353,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> > >       if (busiest->group_type == group_imbalanced)
> > >               goto force_balance;
> > >
> > > +     local = &sds.local_stat;
> > >       /*
> > >        * If the local group is busier than the selected busiest group
> > >        * don't try and pull any tasks.
> > > --
> > > 2.34.1
> > >