linux-kernel - Re: [RFC PATCH 5/6] sched/uclamp: Remove all uclamp bucket logic

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Date:   Fri, 3 Nov 2023 14:50:36 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Hongyan Xia <Hongyan.Xia2@....com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Qais Yousef <qyousef@...alina.io>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Lukasz Luba <lukasz.luba@....com>,
        Christian Loehle <christian.loehle@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/6] sched/uclamp: Remove all uclamp bucket logic

On 04/10/2023 11:04, Hongyan Xia wrote:
> From: Hongyan Xia <hongyan.xia2@....com>
> 
> Also rewrite uclamp_update_active() so that the effective uclamp values
> are updated every time we change task group properties, change system
> defaults or a request is issued from userspace.

Tested it with

# cgcreate -g cpu:/A
# echo $$ > /sys/fs/cgroup/cpu/A/tasks

(1) per-task

# uclampset --pid $$  -m 256 -M 768

(2) per taskgroup

# echo 25.0 > /sys/fs/cgroup/cpu/A/cpu.uclamp.min
# echo 75.0 > /sys/fs/cgroup/cpu/A/cpu.uclamp.max

(3) system-wide

# echo 256 > /proc/sys/kernel/sched_util_clamp_min
# echo 768 > /proc/sys/kernel/sched_util_clamp_max

uclamp_update_active() -> uclamp_update_active_nolock() is called in all
cases.

[...]

uclamp_eff_get()'s function header still mentions `clamp bucket index`.

> @@ -1542,196 +1485,24 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
>  
>  unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
>  {
> -	struct uclamp_se uc_eff;
> -
> -	/* Task currently refcounted: use back-annotated (effective) value */
> -	if (p->uclamp[clamp_id].active)
> -		return (unsigned long)p->uclamp[clamp_id].value;
> -
> -	uc_eff = uclamp_eff_get(p, clamp_id);
> -
> -	return (unsigned long)uc_eff.value;
> -}

[...]