Messages in this thread | | | From | Joel Fernandes <> | Date | Sat, 10 Jun 2017 02:26:27 -0700 | Subject | Re: [PATCH 3/3] cpufreq: intel_pstate: Provide resolve_freq() to fix regression |
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On Fri, Jun 9, 2017 at 3:15 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > When the schedutil governor calls cpufreq_driver_resolve_freq() for the > intel_pstate (in passive mode) driver, it simply returns the requested > frequency as there is no ->resolve_freq() callback provided. > > The result is that get_next_freq() doesn't get a chance to know the > frequency which will be set eventually and we can hit a potential > regression as explained in the following paragraph. > > 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, the intel_pstate driver will end up setting the > frequency as 1.1 GHz. > > Though the sg_policy->next_freq field gets updated with the average > frequency only. And so we will finally select the min frequency when the > next_freq is 1 more than the min frequency as the average then will be > equal to the min frequency. But that will also take lots of iterations > of the schedutil update callbacks. > > Fix that by providing a resolve_freq() callback. > > Tested on desktop with Intel Skylake processors. > > Fixes: 39b64aa1c007 ("cpufreq: schedutil: Reduce frequencies slower") > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > --- > drivers/cpufreq/intel_pstate.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c > index 029a93bfb558..e177352180c3 100644 > --- a/drivers/cpufreq/intel_pstate.c > +++ b/drivers/cpufreq/intel_pstate.c > @@ -2213,6 +2213,19 @@ static int intel_cpufreq_target(struct cpufreq_policy *policy, > return 0; > } > > +unsigned int intel_cpufreq_resolve_freq(struct cpufreq_policy *policy, > + unsigned int target_freq)
Should be defined as static?
Thanks, Joel
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