On 10-06-17, 02:26, Joel Fernandes wrote: > On Fri, Jun 9, 2017 at 3:15 AM, Viresh Kumar <[email protected]> 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 <[email protected]> > > --- > > 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?
Yes. -- viresh
