On Wednesday 17 Feb 2021 at 17:10:27 (+0530), Viresh Kumar wrote: > On 17-02-21, 11:30, Ionela Voinescu wrote: > > The problem is not topology_scale_freq_invariant() but whether a scale > > factor is set for some CPUs. > > > > Scenario (test system above): > > - "AMUs" are only supported for [1-2], > > - cpufreq_supports_freq_invariance() -> false > > > > What should happen: > > - topology_scale_freq_invariant() -> false (passed) > > - all CPUs should have their freq_scale unmodified (1024) - (failed) > > because only 2 out of 6 CPUs have a method of setting a scale factor > > > > What does happen: > > - arch_set_freq_tick() -> topology_set_freq_tick() will set a scale > > factor for [1-2] based on AMUs. This should not happen. We will end > > up with invariant signals for bigs and signals that are not freq > > invariant for littles. > > Another case. cpufreq is included as a module and AMU is implemented > partially. > > - first time cpufreq driver is inserted, we set up everything and > freq_scale gets updated on ticks. > > - remove cpufreq driver, we are back in same situation. >
Yes, but the littles (lacking AMUs) would have had a scale factor set through arch_set_freq_scale() which will correspond to the last frequency change through the cpufreq driver. When removing the driver, it's unlikely that the frequency of littles will change (no driver). - topology_scale_freq_invariant() will still return true. - littles would still have a scale factor set which is likely accurate - bigs will continue updating the scale factor through AMUs. See a very useful comment someone added recently :) : """ + /* + * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU + * counters don't have any dependency on cpufreq driver once we have + * initialized AMU support and enabled invariance. The AMU counters will + * keep on working just fine in the absence of the cpufreq driver, and + * for the CPUs for which there are no counters available, the last set + * value of freq_scale will remain valid as that is the frequency those + * CPUs are running at. + */ """ > We can't control it that way.. Or we add another call layer in middle > before the tick-handler gets called for AMU, which will check if we > are fully invariant or not ? > I would avoid additional work done on the tick, especially for a scenario which is unlikely. If you think this case is worth supporting, it might be best to do it at CPUFREQ_REMOVE_POLICY event. Thanks, Ionela. > -- > viresh
