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Date:   Tue, 11 Jul 2023 09:13:41 -0400
From:   Phil Auld <pauld@redhat.com>
To:     Benjamin Segall <bsegall@google.com>
Cc:     linux-kernel@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mel Gorman <mgorman@suse.de>,
        Frederic Weisbecker <frederic@kernel.org>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v5 1/2] sched, cgroup: Restore meaning to
 hierarchical_quota
Message-ID: <20230711131341.GB150804@lorien.usersys.redhat.com>
References: <20230707195748.2918490-1-pauld@redhat.com>
 <20230707195748.2918490-2-pauld@redhat.com>
 <xm26h6qbfhbo.fsf@google.com>
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On Mon, Jul 10, 2023 at 05:00:11PM -0700 Benjamin Segall wrote:
> Phil Auld <pauld@redhat.com> writes:
> 
> > In cgroupv2 cfs_b->hierarchical_quota is set to -1 for all task
> > groups due to the previous fix simply taking the min.  It should
> > reflect a limit imposed at that level or by an ancestor. Even
> > though cgroupv2 does not require child quota to be less than or
> > equal to that of its ancestors the task group will still be
> > constrained by such a quota so this should be shown here. Cgroupv1
> > continues to set this correctly.
> >
> > In both cases, add initialization when a new task group is created
> > based on the current parent's value (or RUNTIME_INF in the case of
> > root_task_group). Otherwise, the field is wrong until a quota is
> > changed after creation and __cfs_schedulable() is called.
> 
> Reviewed-by: Ben Segall <bsegall@google.com>
>

Thanks, I'll hold on to this for the next version where I update the comment
if that's okay. I was just going to send that but based on your comment
on patch 2 may just do a v6 of the whole thing.


Cheers,
Phil

> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index a68d1276bab0..1b214e10c25d 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -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);
> >  		} else {
> >  			if (quota == RUNTIME_INF)
> >  				quota = parent_quota;
> 
> I suppose you could also set RUNTIME_INF to be a positive value or
> better yet just compare at unsigned, but it's not like config needs to
> be fast, so no need to mess with that.
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 373ff5f55884..92381f9ecf37 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6005,13 +6005,14 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> >  	return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
> >  }
> >  
> > -void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> > +void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *parent)
> >  {
> >  	raw_spin_lock_init(&cfs_b->lock);
> >  	cfs_b->runtime = 0;
> >  	cfs_b->quota = RUNTIME_INF;
> >  	cfs_b->period = ns_to_ktime(default_cfs_period());
> >  	cfs_b->burst = 0;
> > +	cfs_b->hierarchical_quota = ((parent) ? parent->hierarchical_quota : RUNTIME_INF);
> 
> Minor style nit: don't need any of these parens here.
> 

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