Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 12 Jun 2017 14:33:03 +0200 | Subject | Re: [PATCH 2/3] cpufreq: schedutil: Fix selection algorithm while reducing frequency |
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On Mon, Jun 12, 2017 at 5:44 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > On 10-06-17, 23:21, Joel Fernandes wrote: >> On Sat, Jun 10, 2017 at 2:11 AM, Joel Fernandes <joelaf@google.com> wrote: >> > On Fri, Jun 9, 2017 at 3:15 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: >> >> While reducing frequency if there are no frequencies available between >> >> "current" and "next" calculated frequency, then the core will never >> >> select the "next" frequency. >> >> >> >> For example, consider the possible range of frequencies as 900 MHz, 1 >> >> GHz, 1.1 GHz, and 1.2 GHz. If the current frequency is 1.1 GHz and the >> >> next frequency (based on current utilization) is 1 GHz, then the >> >> schedutil governor will try to set the average of these as the next >> >> frequency (i.e. 1.05 GHz). >> >> >> >> Because we always try to find the lowest frequency greater than equal to >> >> the target frequency, cpufreq_driver_resolve_freq() will end up >> >> returning 1.1 GHz only. And we will not be able to reduce the frequency >> >> eventually. The worst hit is the policy->min frequency as that will >> >> never get selected after the frequency is increased once. >> > >> > But once utilization goes to 0, it will select the min frequency >> > (because it selects lowest frequency >= target)? >> >> Never mind my comment about util 0, I see the problem you mention. >> However I feel that this entire series adds complexity all to handle >> the case of a false cache-miss which I think might not be that bad, >> and the tradeoff with complexity/readability of the code kind of >> negates the benefit. That's just my opinion about it fwiw. > > Right and that's why I said in the cover letter that we may want to revert the > offending commit for the time being as the solutions provided here have too much > dependency on the resolve_freq() callback.
So I've decided to revert that commit for 4.12.
Thanks, Rafael
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