Messages in this thread | | | Date | Sat, 26 Aug 2023 21:08:29 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH 2/4] sched: cpufreq: Fix apply_dvfs_headroom() escaping uclamp constraints |
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On 08/21/23 18:39, Dietmar Eggemann wrote: > On 20/08/2023 23:06, Qais Yousef wrote: > > DVFS headroom is applied after we calculate the effective_cpu_util() > > which is where we honour uclamp constraints. It makes more sense to > > apply the headroom there once and let all users naturally get the right > > thing without having to sprinkle the call around in various places. > > uclamp is applied in effective_cpu_util(..., FREQUENCY_UTIL, ...) which > IMHO currently has 2 power callers: (1) schedutil: sugov_get_util() and > (2) EAS: eenv_pd_max_util() > > > Before this fix running > > > > uclampset -M 800 cat /dev/zero > /dev/null > > > > Will cause the test system to run at max freq of 2.8GHz. After the fix > > it runs at 2.2GHz instead which is the correct value that matches the > > capacity of 800. > > IMHO, a system at util = 800 (w/o uclamp) would also run at 2.8Ghz since > we would call map_util_to_perf() on 800, no matter from where we call it.
Sorry, I would very strongly disagree here. What you're saying the effective range of uclamp_max is 800 and anything above that will always go to max. How can this be acceptable?
> > > Note that similar problem exist for uclamp_min. If util was 50, and > > uclamp_min is 100. Since we apply_dvfs_headroom() after apply uclamp > > constraints, we'll end up with util of 125 instead of 100. IOW, we get > > boosted twice, first time by uclamp_min, and second time by dvfs > > headroom. > > I see what you want to change here but: > > So far we have `util -> uclamp -> map_util_to_perf()`
:-O
So when I set the system uclamp_max to 800 it will still run at max; and this is normal?!!
> > which is fine when we see uclamp as an entity which constrains util, not > the util after being mapped to a capacity constraint.
-ENOPARSE.
Cheers
-- Qais Yousef
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