From: peterz@infradead.org
To: Juri Lelli <juri.lelli@redhat.com>
Cc: mingo@redhat.com, rostedt@goodmis.org, tglx@linutronix.de,
linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it,
tommaso.cucinotta@santannapisa.it, alessio.balsini@gmail.com,
bristot@redhat.com, dietmar.eggemann@arm.com,
linux-rt-users@vger.kernel.org, mtosatti@redhat.com,
williams@redhat.com, valentin.schneider@arm.com
Subject: Re: [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor
Date: Fri, 7 Aug 2020 12:46:18 +0200 [thread overview]
Message-ID: <20200807104618.GH2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200807095604.GO42956@localhost.localdomain>
On Fri, Aug 07, 2020 at 11:56:04AM +0200, Juri Lelli wrote:
> Starting deadline server for lower priority classes right away when
> first task is enqueued might break guarantees, as tasks belonging to
> intermediate priority classes could be uselessly preempted. E.g., a well
> behaving (non hog) FIFO task can be preempted by NORMAL tasks even if
> there are still CPU cycles available for NORMAL tasks to run, as they'll
> be running inside the fair deadline server for some period of time.
>
> To prevent this issue, implement a starvation monitor mechanism that
> starts the deadline server only if a (fair in this case) task hasn't
> been scheduled for some interval of time after it has been enqueued.
> Use pick/put functions to manage starvation monitor status.
One thing I considerd was scheduling this as a least-laxity entity --
such that it runs late, not early -- and start the server when
rq->nr_running != rq->cfs.h_nr_running, IOW when there's !fair tasks
around.
Not saying we should do it like that, but that's perhaps more
deterministic than this.
next prev parent reply other threads:[~2020-08-07 10:47 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-07 9:50 [RFC PATCH v2 0/6] SCHED_DEADLINE server infrastructure Juri Lelli
2020-08-07 9:50 ` [RFC PATCH v2 1/6] sched: Unify runtime accounting across classes Juri Lelli
2020-08-07 9:50 ` [RFC PATCH v2 2/6] sched/deadline: Collect sched_dl_entity initialization Juri Lelli
2020-08-07 9:50 ` [RFC PATCH v2 3/6] sched/deadline: Move bandwidth accounting into {en,de}queue_dl_entity Juri Lelli
2020-08-07 9:50 ` [RFC PATCH v2 4/6] sched/deadline: Introduce deadline servers Juri Lelli
2020-10-06 7:56 ` luca abeni
2020-10-06 9:35 ` Juri Lelli
2020-10-06 9:51 ` luca abeni
2020-08-07 9:50 ` [RFC PATCH v2 5/6] sched/fair: Add trivial fair server Juri Lelli
2020-08-07 9:56 ` [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor Juri Lelli
2020-08-07 10:46 ` peterz [this message]
2020-08-07 11:30 ` Daniel Bristot de Oliveira
2020-08-07 12:50 ` Juri Lelli
2020-08-07 13:49 ` luca abeni
2020-08-07 14:11 ` peterz
2020-08-07 16:48 ` Daniel Bristot de Oliveira
2020-08-07 13:28 ` luca abeni
2020-08-07 13:43 ` Juri Lelli
2020-08-07 13:55 ` luca abeni
2020-08-07 14:11 ` Juri Lelli
2020-08-07 14:13 ` peterz
2020-08-07 15:06 ` Juri Lelli
2020-08-07 13:16 ` [RFC PATCH v2 0/6] SCHED_DEADLINE server infrastructure luca abeni
2020-08-07 13:30 ` Juri Lelli
2020-08-07 13:41 ` luca abeni
2020-08-07 14:04 ` Juri Lelli
2020-08-07 14:14 ` peterz
2020-09-08 22:22 ` Pavel Machek
2020-09-09 5:51 ` Juri Lelli
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