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Date:   Tue, 8 Jun 2021 19:21:57 +0100
From:   Qais Yousef <qais.yousef@arm.com>
To:     Xuewen Yan <xuewen.yan94@gmail.com>
Cc:     Quentin Perret <qperret@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Benjamin Segall <bsegall@google.com>,
        Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Chunyan Zhang <zhang.lyra@gmail.com>,
        Ryan Y <xuewyan@foxmail.com>,
        Patrick Bellasi <patrick.bellasi@matbug.net>, tj@kernel.org
Subject: Re: [PATCH] sched/uclamp: Avoid setting cpu.uclamp.min bigger than
 cpu.uclamp.max
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On 06/08/21 23:01, Xuewen Yan wrote:
> Hi
> 
> On Tue, Jun 8, 2021 at 10:25 PM Qais Yousef <qais.yousef@arm.com> wrote:
> >
> > --->8---
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9e9a5be35cde..1d2d3e6648a6 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
> >  static inline struct uclamp_se
> >  uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
> >  {
> > -       struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> > +       /* Copy by value as we could modify it */
> > +       struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
> >  #ifdef CONFIG_UCLAMP_TASK_GROUP
> > +       unsigned long tg_min, tg_max, value;
> >
> >         /*
> >          * Tasks in autogroups or root task group will be
> >          * restricted by system defaults.
> >          */
> >         if (task_group_is_autogroup(task_group(p)))
> > -               return uc_req;
> > +               return uc_eff;
> >         if (task_group(p) == &root_task_group)
> > -               return uc_req;
> > +               return uc_eff;
> >
> > -       switch (clamp_id) {
> > -       case UCLAMP_MIN: {
> > -               struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
> > -               if (uc_req.value < uc_min.value)
> > -                       return uc_min;
> > -               break;
> > -       }
> > -       case UCLAMP_MAX: {
> > -               struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> > -               if (uc_req.value > uc_max.value)
> > -                       return uc_max;
> > -               break;
> > -       }
> > -       default:
> > -               WARN_ON_ONCE(1);
> > -               break;
> > -       }
> > +       tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> > +       tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> > +       value = uc_eff.value;
> > +       value = clamp(value, tg_min, tg_max);
> > +       uclamp_se_set(&uc_eff, value, false);
> 
> Is it reasonable to set user_defined to be false here?

Yep, it doesn't really matter for the effective value. It matters for the
actual task request.

> 
> >  #endif
> >
> > -       return uc_req;
> > +       return uc_eff;
> >  }
> >
> >  /*
> > @@ -1661,8 +1651,7 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
> >
> >  #ifdef CONFIG_UCLAMP_TASK_GROUP
> >  static inline void
> > -uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> > -                          unsigned int clamps)
> > +uclamp_update_active_tasks(struct cgroup_subsys_state *css)
> >  {
> >         enum uclamp_id clamp_id;
> >         struct css_task_iter it;
> > @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> >
> >         css_task_iter_start(css, 0, &it);
> >         while ((p = css_task_iter_next(&it))) {
> > -               for_each_clamp_id(clamp_id) {
> > -                       if ((0x1 << clamp_id) & clamps)
> > -                               uclamp_update_active(p, clamp_id);
> > -               }
> > +               for_each_clamp_id(clamp_id)
> > +                       uclamp_update_active(p, clamp_id);
> >         }
> >         css_task_iter_end(&it);
> >  }
> > @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
> >                 }
> >
> >                 /* Immediately update descendants RUNNABLE tasks */
> > -               uclamp_update_active_tasks(css, clamps);
> > +               uclamp_update_active_tasks(css);
> >         }
> >  }
> 
> Would you resend another email? maybe it would be better to resend an
> email with a new subject?

Yeah I will do a proper posting. But I need to stare at this a bit more then
will do.

Thanks

--
Qais Yousef