Messages in this thread Patch in this message | | | Date | Thu, 15 Apr 2021 15:05:26 +0000 | From | Quentin Perret <> | Subject | Re: [PATCH] PM / EM: Inefficient OPPs detection |
| |
On Thursday 15 Apr 2021 at 14:59:54 (+0000), Quentin Perret wrote: > 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
why is it even *exported* then ...
> 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
| |