From: luca abeni <luca.abeni@santannapisa.it>
To: peterz@infradead.org
Cc: Juri Lelli <juri.lelli@redhat.com>,
mingo@redhat.com, rostedt@goodmis.org, tglx@linutronix.de,
linux-kernel@vger.kernel.org, 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 15:49:41 +0200 [thread overview]
Message-ID: <20200807154941.2bb11408@nowhere> (raw)
In-Reply-To: <20200807104618.GH2674@hirez.programming.kicks-ass.net>
Hi Peter,
On Fri, 7 Aug 2020 12:46:18 +0200
peterz@infradead.org wrote:
> 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
Are you thinking about scheduling both RT and non-RT tasks through
deadline servers? If yes, then I think that using something like
laxity-based scheduling for the SCHED_OTHER server can be a good idea
(but then we need to understand how to combine deadline-based
scheduling with laxity-based scheduling, etc...)
Or are you thinking about keeping the SCHED_OTHER server throttled
until its laxity is 0 (or until its laxity is lower than some small
value)? In this second case, the approach would work even if RT tasks
are not scheduled through a server (but I do not know which kind of
performance guarantee we could provide).
> -- and start the server when
> rq->nr_running != rq->cfs.h_nr_running, IOW when there's !fair tasks
> around.
Yes, this could be a good optimization.
Luca
>
> 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 13:50 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
2020-08-07 11:30 ` Daniel Bristot de Oliveira
2020-08-07 12:50 ` Juri Lelli
2020-08-07 13:49 ` luca abeni [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200807154941.2bb11408@nowhere \
--to=luca.abeni@santannapisa.it \
--cc=alessio.balsini@gmail.com \
--cc=bristot@redhat.com \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=mtosatti@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=tommaso.cucinotta@santannapisa.it \
--cc=valentin.schneider@arm.com \
--cc=williams@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).