From: luca abeni <luca.abeni@santannapisa.it>
To: Claudio Scordino <claudio@evidence.eu.com>
Cc: Quentin Perret <quentin.perret@arm.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
viresh kumar <viresh.kumar@linaro.org>,
Valentin Schneider <valentin.schneider@arm.com>
Subject: Re: [PATCH v5 00/10] track CPU utilization
Date: Wed, 6 Jun 2018 22:53:09 +0200 [thread overview]
Message-ID: <20180606225309.24602773@nowhere> (raw)
In-Reply-To: <6c2dc1aa-3e19-be14-0ed8-b29003c72e61@evidence.eu.com>
Hi all,
sorry; I missed the beginning of this thread... Anyway, below I add
some comments:
On Wed, 6 Jun 2018 15:05:58 +0200
Claudio Scordino <claudio@evidence.eu.com> wrote:
[...]
> >> Ok, I see ... Have you guys already tried something like my patch
> >> above (keeping the freq >= this_bw) in real world use cases ? Is
> >> this costing that much energy in practice ? If we fill the gaps
> >> left by DL (when it
> >
> > IIRC, Claudio (now Cc-ed) did experiment a bit with both
> > approaches, so he might add some numbers to my words above. I
> > didn't (yet). But, please consider that I might be reserving (for
> > example) 50% of bandwidth for my heavy and time sensitive task and
> > then have that task wake up only once in a while (but I'll be
> > keeping clock speed up for the whole time). :/
>
> As far as I can remember, we never tested energy consumption of
> running_bw vs this_bw, as at OSPM'17 we had already decided to use
> running_bw implementing GRUB-PA. The rationale is that, as Juri
> pointed out, the amount of spare (i.e. reclaimable) bandwidth in
> this_bw is very user-dependent.
Yes, I agree with this. The appropriateness of using this_bw or
running_bw is highly workload-dependent... If a periodic task consumes
much less than its runtime (or if a sporadic task has inter-activation
times much larger than the SCHED_DEADLINE period), then running_bw has
to be preferred. But if a periodic task consumes almost all of its
runtime before blocking, then this_bw has to be preferred...
But this also depends on the hardware: if the frequency switch time is
small, then running_bw is more appropriate... On the other hand,
this_bw works much better if the frequency switch time is high.
(Talking about this, I remember Claudio measured frequency switch times
large almost 3ms... Is this really due to hardware issues? Or maybe
there is some software issue invoved? 3ms look like a lot of time...)
Anyway, this is why I proposed to use some kind of /sys/... file to
control the kind of deadline utilization used for frequency scaling: in
this way, the system designer / administrator, who hopefully has the
needed information about workload and hardware, can optimize the
frequency scaling behaviour by deciding if running_bw or this_bw will be
used.
Luca
> For example, the user can let this_bw
> be much higher than the measured bandwidth, just to be sure that the
> deadlines are met even in corner cases. In practice, this means that
> the task executes for quite a short time and then blocks (with its
> bandwidth reclaimed, hence the CPU frequency reduced, at the 0lag
> time). Using this_bw rather than running_bw, the CPU frequency would
> remain at the same fixed value even when the task is blocked. I
> understand that on some cases it could even be better (i.e. no waste
> of energy in frequency switch). However, IMHO, these are corner cases
> and in the average case it is better to rely on running_bw and reduce
> the CPU frequency accordingly.
>
> Best regards,
>
> Claudio
prev parent reply other threads:[~2018-06-06 21:53 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-25 13:12 [PATCH v5 00/10] track CPU utilization Vincent Guittot
2018-05-25 13:12 ` [PATCH v5 01/10] sched/pelt: Move pelt related code in a dedicated file Vincent Guittot
2018-05-25 14:26 ` Quentin Perret
2018-05-25 16:14 ` Peter Zijlstra
2018-05-29 8:21 ` Quentin Perret
2018-05-25 18:04 ` Patrick Bellasi
2018-05-29 14:55 ` Quentin Perret
2018-05-29 15:02 ` Vincent Guittot
2018-05-29 15:04 ` Quentin Perret
2018-05-25 13:12 ` [PATCH v5 02/10] sched/rt: add rt_rq utilization tracking Vincent Guittot
2018-05-25 15:54 ` Patrick Bellasi
2018-05-29 13:29 ` Vincent Guittot
2018-05-30 9:32 ` Patrick Bellasi
2018-05-30 10:06 ` Vincent Guittot
2018-05-30 11:01 ` Patrick Bellasi
2018-05-30 14:39 ` Vincent Guittot
2018-05-25 13:12 ` [PATCH v5 03/10] cpufreq/schedutil: add rt " Vincent Guittot
2018-05-30 7:03 ` Viresh Kumar
2018-05-30 8:23 ` Vincent Guittot
2018-05-30 9:40 ` Patrick Bellasi
2018-05-30 9:53 ` Vincent Guittot
2018-05-30 16:46 ` Quentin Perret
2018-05-31 8:46 ` Juri Lelli
2018-06-01 16:23 ` Peter Zijlstra
2018-06-01 17:23 ` Patrick Bellasi
2018-06-04 10:17 ` Quentin Perret
2018-06-04 15:16 ` Patrick Bellasi
2018-05-25 13:12 ` [PATCH v5 04/10] sched/dl: add dl_rq " Vincent Guittot
2018-05-30 10:50 ` Patrick Bellasi
2018-05-30 11:51 ` Vincent Guittot
2018-05-25 13:12 ` [PATCH v5 05/10] cpufreq/schedutil: get max utilization Vincent Guittot
2018-05-28 10:12 ` Juri Lelli
2018-05-28 14:57 ` Vincent Guittot
2018-05-28 15:22 ` Juri Lelli
2018-05-28 16:34 ` Vincent Guittot
2018-05-31 10:27 ` Patrick Bellasi
2018-05-31 13:02 ` Vincent Guittot
2018-06-01 13:53 ` Vincent Guittot
2018-06-01 17:45 ` Joel Fernandes
2018-06-04 6:41 ` Vincent Guittot
2018-06-04 7:04 ` Juri Lelli
2018-06-04 7:14 ` Vincent Guittot
2018-06-04 10:12 ` Juri Lelli
2018-06-04 12:35 ` Vincent Guittot
2018-05-29 5:08 ` Joel Fernandes
2018-05-29 6:31 ` Juri Lelli
2018-05-29 6:48 ` Vincent Guittot
2018-05-29 9:47 ` Juri Lelli
2018-05-29 8:40 ` Quentin Perret
2018-05-29 9:52 ` Juri Lelli
2018-05-30 8:37 ` Quentin Perret
2018-05-30 8:51 ` Juri Lelli
2018-05-25 13:12 ` [PATCH v5 06/10] sched: remove rt and dl from sched_avg Vincent Guittot
2018-05-25 13:12 ` [PATCH v5 07/10] sched/irq: add irq utilization tracking Vincent Guittot
2018-05-30 15:55 ` Dietmar Eggemann
2018-05-30 18:45 ` Vincent Guittot
2018-05-31 16:54 ` Dietmar Eggemann
2018-06-06 16:06 ` Vincent Guittot
2018-06-07 8:29 ` Dietmar Eggemann
2018-06-07 8:44 ` Vincent Guittot
2018-06-07 9:06 ` Dietmar Eggemann
2018-05-25 13:12 ` [PATCH v5 08/10] cpufreq/schedutil: take into account interrupt Vincent Guittot
2018-05-28 10:41 ` Juri Lelli
2018-05-28 12:06 ` Vincent Guittot
2018-05-28 12:37 ` Juri Lelli
2018-05-25 13:12 ` [PATCH v5 09/10] sched: remove rt_avg code Vincent Guittot
2018-05-25 13:12 ` [PATCH v5 10/10] proc/sched: remove unused sched_time_avg_ms Vincent Guittot
2018-06-04 16:50 ` [PATCH v5 00/10] track CPU utilization Peter Zijlstra
2018-06-04 17:13 ` Quentin Perret
2018-06-04 18:08 ` Vincent Guittot
2018-06-05 14:18 ` Peter Zijlstra
2018-06-05 15:03 ` Juri Lelli
2018-06-05 15:38 ` Patrick Bellasi
2018-06-05 22:27 ` Peter Zijlstra
2018-06-06 9:44 ` Quentin Perret
2018-06-06 9:59 ` Vincent Guittot
2018-06-06 10:02 ` Vincent Guittot
2018-06-06 10:12 ` Quentin Perret
2018-06-05 8:36 ` Vincent Guittot
2018-06-05 10:57 ` Quentin Perret
2018-06-05 11:59 ` Vincent Guittot
2018-06-05 13:12 ` Quentin Perret
2018-06-05 13:18 ` Vincent Guittot
2018-06-05 13:52 ` Quentin Perret
2018-06-05 13:55 ` Vincent Guittot
2018-06-05 14:09 ` Quentin Perret
2018-06-05 14:21 ` Quentin Perret
2018-06-05 12:11 ` Juri Lelli
2018-06-05 13:05 ` Quentin Perret
2018-06-05 13:15 ` Juri Lelli
2018-06-05 14:01 ` Quentin Perret
2018-06-05 14:13 ` Juri Lelli
2018-06-06 13:05 ` Claudio Scordino
2018-06-06 13:20 ` Quentin Perret
2018-06-06 13:53 ` Claudio Scordino
2018-06-06 14:10 ` Quentin Perret
2018-06-06 21:05 ` luca abeni
2018-06-07 8:25 ` Quentin Perret
2018-06-06 20:53 ` luca abeni [this message]
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