Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 13 Nov 2019 10:44:39 +0100
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com, glenn@aurora.tech, linux-kernel@vger.kernel.org,
        rostedt@goodmis.org, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, tglx@linutronix.de,
        luca.abeni@santannapisa.it, c.scordino@evidence.eu.com,
        tommaso.cucinotta@santannapisa.it, bristot@redhat.com
Subject: Re: [PATCH 2/2] sched/deadline: Temporary copy static parameters to
 boosted non-DEADLINE entities
Message-ID: <20191113094439.GC29273@localhost.localdomain>
References: <20191112075056.19971-1-juri.lelli@redhat.com>
 <20191112075056.19971-3-juri.lelli@redhat.com>
 <20191112105130.GZ4131@hirez.programming.kicks-ass.net>
 <20191113092241.GB29273@localhost.localdomain>
 <20191113093649.GI4131@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
In-Reply-To: <20191113093649.GI4131@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.11.3 (2019-02-01)
Content-Type: text/plain; charset=WINDOWS-1252
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 13/11/19 10:36, Peter Zijlstra wrote:
> On Wed, Nov 13, 2019 at 10:22:41AM +0100, Juri Lelli wrote:
>=20
> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index 26e4ffa01e7a..16164b0ba80b 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -4452,9 +4452,11 @@ void rt_mutex_setprio(struct task_struct *p, s=
truct task_struct *pi_task)
> > >  =09=09if (!dl_prio(p->normal_prio) ||
> > >  =09=09    (pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
> > >  =09=09=09p->dl.dl_boosted =3D 1;
> > > -=09=09=09queue_flag |=3D ENQUEUE_REPLENISH;
> > > -=09=09} else
> > > +=09=09=09p->dl.deadline =3D pi_task->dl.deadline;
> > > +=09=09} else {
> > >  =09=09=09p->dl.dl_boosted =3D 0;
> > > +=09=09=09p->dl.deadline =3D p->dl.normal_deadline;
> > > +=09=09}
> > >  =09=09p->sched_class =3D &dl_sched_class;
> > >  =09} else if (rt_prio(prio)) {
> > >  =09=09if (dl_prio(oldprio))
>=20
> > So, the problem is more related to pi_se->dl_runtime than its deadline.
> > Even if we don't replenish at the instant in time when boosting happens=
,
> > the boosted task might still deplete its runtime while being boosted an=
d
>=20
> I thought we ignored all runtime checks when we were boosted? Yes, that

We don't throttle and replenish instantly when runtime is depleted, but
we still account runtime. See update_curr_dl(), dl_runtime_exceeded()
and if(unlikely(dl_se->dl_boosted ...) case.

Mmm, maybe we should stop accounting as well and only postpone
deadlines, is this what you had in mind?

> is all sorts of broken, but IIRC we figured that barring something like
> proxy-execution there really wasn't anything sane we could do wrt
> bandwidth anyway.
>=20
> Seeing how proper bandwidth handling would have the boosted task consume
> the boostee's budget etc.. And blocking the entire boost chain when it
> collectively runs out.

Yep, this is how it should eventually all work.