On Wednesday 29 Jan 2020 at 20:37:41 (+0100), Peter Zijlstra wrote: > On Wed, Dec 18, 2019 at 06:26:06PM +0000, Ionela Voinescu wrote: > > To be noted that this patch is a temporary one. It introduces the > > interface added by the patches at [1] to allow update of the frequency > > invariance scale factor based on counters. If [1] is merged there is > > not need for this patch. > > > > For platforms that support counters (x86 - APERF/MPERF, arm64 - AMU > > counters) the frequency invariance correction factor can be obtained > > using a core counter and a fixed counter to get information on the > > performance (frequency based only) obtained in a period of time. This > > will more accurately reflect the actual current frequency of the CPU, > > compared with the alternative implementation that reflects the request > > of a performance level from the OS through the cpufreq framework > > (arch_set_freq_scale). > > > > Therefore, introduce an interface - arch_scale_freq_tick, to be > > implemented by each architecture and called for each CPU on the tick > > to update the scale factor based on the delta in the counter values, > > if counter support is present on the CPU. > > > > Either because reading counters is expensive or because reading > > counters from remote CPUs is not possible or is expensive, only > > update the counter based frequency scale factor on the tick for > > now. A tick based update will definitely be necessary either due to > > it being the only point of update for certain architectures or in > > order to cache the counter values for a particular CPU, if a > > further update from that CPU is not possible. > > > > [1] > > https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@xxxxxxx/ > > FWIW, those patches just landed in tip/sched/core Thanks, Peter, I'll drop this one next time around. Ionela.
