lkml.org 
[lkml]   [2021]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] PM / EM: Inefficient OPPs detection
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

\
 
 \ /
  Last update: 2021-04-15 17:09    [W:0.051 / U:0.964 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site