On Thursday 15 Apr 2021 at 15:34:53 (+0100), Vincent Donnefort wrote: > On Thu, Apr 15, 2021 at 01:16:35PM +0000, Quentin Perret wrote: > > On Thursday 08 Apr 2021 at 18:10:29 (+0100), Vincent Donnefort wrote: > > > --- a/kernel/sched/cpufreq_schedutil.c > > > +++ b/kernel/sched/cpufreq_schedutil.c > > > @@ -10,6 +10,7 @@ > > > > > > #include "sched.h" > > > > > > +#include <linux/energy_model.h> > > > #include <linux/sched/cpufreq.h> > > > #include <trace/events/power.h> > > > > > > @@ -164,6 +165,9 @@ static unsigned int get_next_freq(struct sugov_policy > > > *sg_policy, > > > > > > freq = map_util_freq(util, freq, max); > > > > > > + /* Avoid inefficient performance states */ > > > + freq = em_pd_get_efficient_freq(em_cpu_get(policy->cpu), freq); > > > > I remember this was discussed when Douglas sent his patches some time > > ago, but I still find it sad we index the EM table here but still > > re-index the cpufreq frequency table later :/ > > > > Yes in your case this lookup is very inexpensive, but still. EAS relies > > on the EM's table matching cpufreq's accurately, so this second lookup > > still feels rather unnecessary ... > > To get only a single lookup, we would need to bring the inefficiency knowledge > directly to the cpufreq framework. But it has its own limitations: > > The cpufreq driver can have its own resolve_freq() callback, which means > that > not all the drivers would benefit from that feature. > > The cpufreq_table can be ordered and accessed in several ways which brings > many combinations that would need to be supported, ending-up with something > much more intrusive. (We can though decide to limit the feature to the low > to > high access that schedutil needs). > > As the EM needs schedutil to exist anyway, it seemed to be the right place for > this code. It allows any cpufreq driver to benefit from the feature, simplify > a > potential extension for a usage by devfreq devices and as a bonus it speeds-up > energy computing, allowing a more complex Energy Model.
I was thinking of something a bit simpler. cpufreq_driver_resolve_freq appears to be used only from schedutil (why is it even then?), so we could just pull it into cpufreq_schedutil.c and just plain skip the call to cpufreq_frequency_table_target if the target freq has been indexed in the EM table -- it should already be matching a real OPP. Thoughts? Quentin
