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Message-ID: <20220727160501.m4omtncl5nvqoh3p@wubuntu>
Date: Wed, 27 Jul 2022 17:05:01 +0100
From: Qais Yousef <qais.yousef@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ingo Molnar <mingo@...nel.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
linux-kernel@...r.kernel.org, Xuewen Yan <xuewen.yan94@...il.com>,
Wei Wang <wvw@...gle.com>,
Jonathan JMChen <Jonathan.JMChen@...iatek.com>,
Hank <han.lin@...iatek.com>
Subject: Re: [PATCH 2/7] sched/uclamp: Make task_fits_capacity() use
util_fits_cpu()
Hi Vincent
On 07/22/22 10:19, Vincent Guittot wrote:
> Le jeudi 21 juil. 2022 � 15:29:49 (+0100), Qais Yousef a �crit :
> > On 07/12/22 11:48, Qais Yousef wrote:
> > > On 07/11/22 15:09, Vincent Guittot wrote:
> > > > On Wed, 29 Jun 2022 at 21:48, Qais Yousef <qais.yousef@....com> wrote:
> > >
>
> [...]
>
> > > > > @@ -9108,7 +9125,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> > > > >
> > > > > /* Check if task fits in the group */
> > > > > if (sd->flags & SD_ASYM_CPUCAPACITY &&
> > > > > - !task_fits_capacity(p, group->sgc->max_capacity)) {
> > > > > + !task_fits_cpu(p, group->sgc->max_capacity_cpu)) {
> > > >
> > > > All the changes and added complexity above for this line. Can't you
> > > > find another way ?
> > >
> > > You're right, I might have got carried away trying to keep the logic the same.
> > >
> > > Can we use group->asym_prefer_cpu or pick a cpu from group->sgc->cpumask
> > > instead?
> > >
> > > I'll dig more into it anyway and try to come up with simpler alternative.
> >
> > Actually we can't.
> >
> > I can keep the current {max,min}_capacity field and just add the new
> > {max,min}_capacity_cpu and use them where needed. Should address your concerns
> > this way? That was actually the first version of the code, but then it seemed
> > redundant to keep both {max,min}_capacity and {max,min}_capacity_cpu.
> >
> > OR
> >
> > I can add a new function to search for max spare capacity cpu in the group.
> >
> > Preference?
> >
>
> Isn't the below enough and much simpler ?
Thanks for that!
>
> [PATCH] sched/uclamp: Make task_fits_capacity() use util_fits_cpu()
>
> So that the new uclamp rules in regard to migration margin and capacity
> pressure are taken into account correctly.
> ---
> kernel/sched/fair.c | 25 +++++++++++++++----------
> kernel/sched/sched.h | 9 +++++++++
> 2 files changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5eecae32a0f6..3e0c7cc490be 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4317,10 +4317,12 @@ static inline int util_fits_cpu(unsigned long util,
> return fits;
> }
>
> -static inline int task_fits_capacity(struct task_struct *p,
> - unsigned long capacity)
> +static inline int task_fits_cpu(struct task_struct *p, int cpu)
> {
> - return fits_capacity(uclamp_task_util(p), capacity);
> + 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);
> }
>
> static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> @@ -4333,7 +4335,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> return;
> }
>
> - if (task_fits_capacity(p, capacity_of(cpu_of(rq)))) {
> + if (task_fits_cpu(p, cpu_of(rq))) {
> rq->misfit_task_load = 0;
> return;
> }
> @@ -8104,7 +8106,7 @@ static int detach_tasks(struct lb_env *env)
>
> case migrate_misfit:
> /* This is not a misfit task */
> - if (task_fits_capacity(p, capacity_of(env->src_cpu)))
> + if (task_fits_cpu(p, env->src_cpu))
> goto next;
>
> env->imbalance = 0;
> @@ -9085,6 +9087,10 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
>
> memset(sgs, 0, sizeof(*sgs));
>
> + /* Assume that task can't fit any CPU of the group */
> + if (sd->flags & SD_ASYM_CPUCAPACITY)
> + sgs->group_misfit_task_load = 0;
Should this be
sgs->group_misfit_task_load = 1
to indicate it doesn't fit?
> +
> for_each_cpu(i, sched_group_span(group)) {
> struct rq *rq = cpu_rq(i);
> unsigned int local;
> @@ -9104,12 +9110,11 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> if (!nr_running && idle_cpu_without(i, p))
> sgs->idle_cpus++;
>
> - }
> + /* Check if task fits in the CPU */
> + if (sd->flags & SD_ASYM_CPUCAPACITY &&
> + task_fits_cpu(p, i))
> + sgs->group_misfit_task_load = 0;
So we clear the flag if there's any cpu that fits, I think that should work,
yes and much better too. I got tunneled visioned and didn't take a step back to
look at the big picture. Thanks for the suggestion :-)
I think we can make it more efficient by checking if
sgs->group_misfit_task_load is set
/* Check if task fits in the CPU */
if (sd->flags & SD_ASYM_CPUCAPACITY &&
sgs->group_misfit_task_load &&
task_fits_cpu(p, i))
sgs->group_misfit_task_load = 0;
which will avoid calling task_fits_cpu() repeatedly if we got a hit already.
Thanks!
--
Qais Yousef
>
> - /* Check if task fits in the group */
> - if (sd->flags & SD_ASYM_CPUCAPACITY &&
> - !task_fits_capacity(p, group->sgc->max_capacity)) {
> - sgs->group_misfit_task_load = 1;
> }
>
> sgs->group_capacity = group->sgc->capacity;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 02c970501295..3292ad2db4ac 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2988,6 +2988,15 @@ static inline bool uclamp_is_used(void)
> return static_branch_likely(&sched_uclamp_used);
> }
> #else /* CONFIG_UCLAMP_TASK */
> +static inline unsigned long uclamp_eff_value(struct task_struct *p,
> + enum uclamp_id clamp_id)
> +{
> + if (clamp_id == UCLAMP_MIN)
> + return 0;
> +
> + return SCHED_CAPACITY_SCALE;
> +}
> +
> static inline
> unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> struct task_struct *p)
> --
> 2.17.1
>
> >
> > Thanks!
> >
> > --
> > Qais Yousef
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