Messages in this thread | | | Date | Mon, 21 Nov 2016 12:48:02 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits |
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On Mon, Nov 21, 2016 at 05:00:16PM +0530, Viresh Kumar wrote: > On 21-11-16, 12:12, Peter Zijlstra wrote: > > I think it should be replaced by a value provided by the driver. It > > makes sense to have a rate-limit in so far as that it doesn't make sense > > to try and program the hardware faster than it can actually change > > frequencies and/or have a programming cost amortization. And this very > > clearly is a driver specific thing. > > We already have something called as transition_latency for that (though it isn't > used much currently). > > > It however doesn't make sense to me to fudge with this in order to > > achieve ramp up/down differences. > > So if a platform, for example, can do DVFS in say 100-500 us, then the scheduler > should try to re-evaluate frequency (and update it) after that short of a > period? Wouldn't that scheme waste lots of time doing just freq updates? And > that's the primary reason why cpufreq governors have some sort of sampling-rate > or rate-limit until now.
Dunno.. there's of course the cost amortization, but by the time we've reached sugov_should_update_freq() most of the 'expensive' parts have already been done from the scheduler's POV and its once again down to the driver.
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