Messages in this thread | | | Date | Tue, 15 Dec 2015 13:20:15 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity |
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On Tue, Dec 15, 2015 at 09:50:14AM +0100, Luca Abeni wrote: > On 12/15/2015 05:59 AM, Vincent Guittot wrote:
> >The 2nd definition is used to compute the remaining capacity for the > >CFS scheduler. This one doesn't need to be updated at each wake/sleep > >of a deadline task but should reflect the capacity used by deadline in > >a larger time scale. The latter will be used by the CFS scheduler at > >the periodic load balance pace
> Ok, so as I wrote above this really looks like an average utilisation. > My impression (but I do not know the CFS code too much) is that the mainline > kernel is currently doing the right thing to compute it, so maybe there is no > need to change the current code in this regard. > If the current code is not acceptable for some reason, an alternative would > be to measure the active utilisation for frequency scaling, and then apply a > low-pass filter to it for CFS.
So CFS really only needs a 'vague' average idea on how much time it will not get. Its best effort etc., so being a little wrong isn't a problem.
The current code suffices, but I think the reason its been changed in this series is that they want/need separate tracking for fifo/rr and deadline in the next patch, and taking out deadline like proposed was the easiest way of achieving that.
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