linux-kernel - Re: [PATCH v5 1/2] sched, cgroup: Restore meaning to hierarchical

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Message-ID: <ZKxnRIZQzyVDMZGD@slm.duckdns.org>
Date:   Mon, 10 Jul 2023 10:17:08 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Phil Auld <pauld@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Valentin Schneider <vschneid@...hat.com>,
        Ben Segall <bsegall@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v5 1/2] sched, cgroup: Restore meaning to
 hierarchical_quota

Hello,

On Fri, Jul 07, 2023 at 03:57:47PM -0400, Phil Auld wrote:
> @@ -11038,11 +11038,14 @@ static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
>  
>  		/*
>  		 * Ensure max(child_quota) <= parent_quota.  On cgroup2,
> -		 * always take the min.  On cgroup1, only inherit when no
> -		 * limit is set:
> +		 * always take the non-RUNTIME_INF min.  On cgroup1, only
> +		 * inherit when no limit is set:
>  		 */
>  		if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
> -			quota = min(quota, parent_quota);
> +			if (quota == RUNTIME_INF)
> +				quota = parent_quota;
> +			else if (parent_quota != RUNTIME_INF)
> +				quota = min(quota, parent_quota);

Can you please add a comment explaining how hierarchical_quota is used in
cgroup2? It seems like you're using it to detect whether bw limit is
enforced for a given cgroup, which is fine, but the above code in isolation
looks a bit curious because it doesn't serve any purpose by itself.

Thanks.

-- 
tejun