Re: [PATCH] sched/uclamp: Avoid setting cpu.uclamp.min bigger than cpu.uclamp.max

From: Xuewen Yan <xuewen.yan94@gmail.com>
To: Qais Yousef <qais.yousef@arm.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
Date: Tue, 8 Jun 2021 23:01:59 +0800	[thread overview]
Message-ID: <CAB8ipk_w9JeFmbjSOFR-GnaPNiAoFt8f30Oxh3fZRw58wDXo4w@mail.gmail.com> (raw)
In-Reply-To: <20210608142554.tbiu2s5qnwflmk27@e107158-lin.cambridge.arm.com>

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?

>  #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?

BR
xuewen