From: luca abeni <luca.abeni@santannapisa.it>
To: Juri Lelli <juri.lelli@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Wei Wang <wvw@google.com>, Quentin Perret <qperret@google.com>,
Alessio Balsini <balsini@google.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
Patrick Bellasi <patrick.bellasi@matbug.net>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/6] sched/deadline: Implement fallback mechanism for !fit case
Date: Mon, 27 Apr 2020 16:17:15 +0200 [thread overview]
Message-ID: <20200427161715.3dd3a148@nowhere> (raw)
In-Reply-To: <20200427133438.GA6469@localhost.localdomain>
Hi Juri,
On Mon, 27 Apr 2020 15:34:38 +0200
Juri Lelli <juri.lelli@redhat.com> wrote:
> Hi,
>
> On 27/04/20 10:37, Dietmar Eggemann wrote:
> > From: Luca Abeni <luca.abeni@santannapisa.it>
> >
> > When a task has a runtime that cannot be served within the
> > scheduling deadline by any of the idle CPU (later_mask) the task is
> > doomed to miss its deadline.
> >
> > This can happen since the SCHED_DEADLINE admission control
> > guarantees only bounded tardiness and not the hard respect of all
> > deadlines. In this case try to select the idle CPU with the largest
> > CPU capacity to minimize tardiness.
> >
> > Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it>
> > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
[...]
> > - if (!cpumask_empty(later_mask))
> > - return 1;
> > + if (cpumask_empty(later_mask))
> > + cpumask_set_cpu(max_cpu, later_mask);
>
> Think we touched upon this during v1 review, but I'm (still?)
> wondering if we can do a little better, still considering only free
> cpus.
>
> Can't we get into a situation that some of the (once free) big cpus
> have been occupied by small tasks and now a big task enters the
> system and it only finds small cpus available, were it could have fit
> into bigs if small tasks were put onto small cpus?
>
> I.e., shouldn't we always try to best fit among free cpus?
Yes; there was an additional patch that tried schedule each task on the
slowest core where it can fit, to address this issue.
But I think it will go in a second round of patches.
Luca
next prev parent reply other threads:[~2020-04-27 14:17 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-27 8:37 [PATCH v2 0/6] Capacity awareness for SCHED_DEADLINE Dietmar Eggemann
2020-04-27 8:37 ` [PATCH v2 1/6] sched/topology: Store root domain CPU capacity sum Dietmar Eggemann
2020-04-27 8:37 ` [PATCH v2 2/6] sched/deadline: Optimize dl_bw_cpus() Dietmar Eggemann
2020-04-30 10:55 ` Pavan Kondeti
2020-05-01 16:12 ` Dietmar Eggemann
2020-04-27 8:37 ` [PATCH v2 3/6] sched/deadline: Add dl_bw_capacity() Dietmar Eggemann
2020-05-06 10:54 ` Dietmar Eggemann
2020-05-06 12:37 ` Juri Lelli
2020-05-06 15:09 ` Dietmar Eggemann
2020-05-11 8:01 ` Juri Lelli
2020-05-12 12:39 ` Dietmar Eggemann
2020-05-15 12:26 ` Juri Lelli
2020-04-27 8:37 ` [PATCH v2 4/6] sched/deadline: Improve admission control for asymmetric CPU capacities Dietmar Eggemann
2020-04-27 8:37 ` [PATCH v2 5/6] sched/deadline: Make DL capacity-aware Dietmar Eggemann
2020-04-30 13:10 ` Pavan Kondeti
2020-05-01 16:12 ` Dietmar Eggemann
2020-05-04 3:58 ` Pavan Kondeti
2020-05-05 18:02 ` Dietmar Eggemann
2020-04-27 8:37 ` [PATCH v2 6/6] sched/deadline: Implement fallback mechanism for !fit case Dietmar Eggemann
2020-04-27 13:34 ` Juri Lelli
2020-04-27 14:17 ` luca abeni [this message]
2020-04-29 17:39 ` Dietmar Eggemann
2020-04-30 11:00 ` Pavan Kondeti
2020-05-01 16:12 ` Dietmar Eggemann
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