Re: [PATCH v4 7/7] cpufreq: schedutil: New governor based on scheduler utilization data

Rafael J. Wysocki
2016-03-16T21:42:43Z

On Wednesday, March 16, 2016 06:35:41 PM Peter Zijlstra wrote:
> On Wed, Mar 16, 2016 at 03:59:18PM +0100, Rafael J. Wysocki wrote:
>
> > +static unsigned int get_next_freq(struct cpufreq_policy *policy,
> > + unsigned long util, unsigned long max)
> > +{
> > + unsigned int freq = arch_scale_freq_invariant() ?
> > + policy->cpuinfo.max_freq : policy->cur;
> > +
> > + return (freq + (freq >> 2)) * util / max;
> > +}
> > +
> > +static void sugov_update_single(struct update_util_data *hook, u64 time,
> > + unsigned long util, unsigned long max)
> > +{
> > + struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
> > + struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> > + struct cpufreq_policy *policy = sg_policy->policy;
> > + unsigned int next_f;
> > +
> > + if (!sugov_should_update_freq(sg_policy, time))
> > + return;
> > +
> > + next_f = util <= max ?
> > + get_next_freq(policy, util, max) : policy->cpuinfo.max_freq;
>
> I'm not sure that is correct, would not something like this be more
> accurate?
>
> if (util > max)
> util = max;
> next_f = get_next_freq(policy, util, max);
>
> After all, if we clip util we will still only increment to the next freq
> with our multiplication factor.
>
> Hmm, or was this meant to deal with the DL/RT stuff?

Yes, it was.

> Would then not something like:
>
> /* ULONG_MAX is used to force max_freq for Real-Time policies */
> if (util == ULONG_MAX) {
> next_f = policy->cpuinfo.max_freq;
> } else {
> if (util > max)

That cannot happen given the way CFS deals with max before passing it
to cpufreq_update_util().

> util = max;
> next_f = get_next_freq(policy, util, max);
> }
>
> Be clearer?
>
> > + sugov_update_commit(sg_policy, time, next_f);
> > +}

So essentially I can replace the util > max check with the util == ULONG_MAX one
(here and in some other places) if that helps to understand the code, but
functionally that won't change anything.