On Tue, Aug 6, 2019 at 6:10 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > On 02-08-19, 11:28, Rafael J. Wysocki wrote: > > On Friday, August 2, 2019 11:17:55 AM CEST Rafael J. Wysocki wrote: > > > On Fri, Aug 2, 2019 at 7:44 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > > > > > > > Intel pstate driver exposes min_perf_pct and max_perf_pct sysfs files, > > > > which can be used to force a limit on the min/max P state of the driver. > > > > Though these files eventually control the min/max frequencies that the > > > > CPUs will run at, they don't make a change to policy->min/max values. > > > > > > That's correct. > > > > > > > When the values of these files are changed (in passive mode of the > > > > driver), it leads to calling ->limits() callback of the cpufreq > > > > governors, like schedutil. On a call to it the governors shall > > > > forcefully update the frequency to come within the limits. > > > > > > OK, so the problem is that it is a bug to invoke the governor's ->limits() > > > callback without updating policy->min/max, because that's what > > > "limits" mean to the governors. > > > > > > Fair enough. > > > > AFAICS this can be addressed by adding PM QoS freq limits requests of each CPU to > > intel_pstate in the passive mode such that changing min_perf_pct or max_perf_pct > > will cause these requests to be updated. > > Right, that sounds like a good plan. > > But that will never make it to the stable kernels as there will be a > long dependency of otherwise unrelated patches to get that done. My > initial thought was to get this patch merged as it is and then later > migrate to QoS, but since this patch doesn't fix ondemand and > conservative, this patch isn't good enough as well. Right. > Maybe we should add the regular notifier based solution first, mark it > for stable kernels, and then add the QoS specific solution ? I'm not sure if -stable kernels really need a fix here. Let's just make sure that the mainline is OK and let's go straight for the final approach.
