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Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity
Date 2015-12-15 13:50 +0100
Message-ID <qFXdg-4aK-19@gated-at.bofh.it> (permalink)
References (1 earlier) <qDGqe-4EB-21@gated-at.bofh.it> <qFD4T-7Rv-47@gated-at.bofh.it> <qFDHA-86S-23@gated-at.bofh.it> <qFEDE-gS-9@gated-at.bofh.it> <qFPIJ-7DU-7@gated-at.bofh.it>
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On Tue, Dec 15, 2015 at 05:43:44AM +0100, Vincent Guittot wrote:
> On 14 December 2015 at 17:51, Peter Zijlstra <peterz@infradead.org> wrote:

> > No, since the WCET can and _will_ happen, its the best you can do with
> > cpufreq. If you were to set it lower you could not be able to execute
> > correctly in your 'never' tail cases.
> 
> In the context of frequency scaling, This mean that we will never
> reach low frequency

Only if you've stuffed your machine full of deadline tasks, if you take
Luca's example of the I/B frame decoder thingy, then even the WCET for
the I frames should not be very much (albeit significantly more than B
frames).

So while the WCET is pessimistic compared to the avg case, most CPUs can
do video decoding without much effort at all, so even the WCET for the
I-frames might allow us to drop to the lowest cpufreq.

Now, if you were to decode 10 streams at the same time, different story
of course ;-)
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Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-14 16:20 +0100
  Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-14 17:00 +0100
    Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Juri Lelli <Juri.Lelli@arm.com> - 2015-12-14 17:10 +0100
      Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-14 22:20 +0100
    Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-14 18:00 +0100
      Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-14 22:40 +0100
        Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-15 13:40 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 14:40 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-15 14:50 +0100
              Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 22:30 +0100
                Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Juri Lelli <Juri.Lelli@arm.com> - 2015-12-16 10:30 +0100
      Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 05:50 +0100
        Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-15 13:50 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 14:00 +0100
    Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-14 22:20 +0100
      Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 06:10 +0100
        Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 10:00 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-15 13:30 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 13:50 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 14:20 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Peter Zijlstra <peterz@infradead.org> - 2015-12-15 13:30 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 14:30 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 13:50 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 14:40 +0100
          Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 14:00 +0100
            Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in  scale_rt_capacity Luca Abeni <luca.abeni@unitn.it> - 2015-12-15 14:50 +0100

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