On Tue, 9 Oct 2018 at 09:47, Rafael J. Wysocki <raf...@kernel.org> wrote:
>
> On Mon, Oct 8, 2018 at 5:11 PM Waldemar Rymarkiewicz
> <waldemar.rymarkiew...@gmail.com> wrote:
> >
> > From: Waldemar Rymarkiewicz <waldemarx.rymarkiew...@intel.com>
> >
> > The governor updates dbs_info->requested_freq only after increasing or
> > decreasing frequency. There is, however, an use case when this is not
> > sufficient.
> >
> > Imagine, external module constraining cpufreq policy in a way that
> > policy->max
>
> Is the "external module" here a utility or a demon running in user space?
No, this is a driver that communicates with a firmware and makes sure
CPU is running at the highest rate in specific time.
It uses verify_within_limits and update_policy, a standard way to
constraint cpufreq policy limits.
> > @@ -136,10 +135,10 @@ static unsigned int cs_dbs_update(struct
> > cpufreq_policy *policy)
> > requested_freq = policy->min;
> >
> > __cpufreq_driver_target(policy, requested_freq,
> > CPUFREQ_RELATION_L);
> > - dbs_info->requested_freq = requested_freq;
> > }
> >
> > out:
> > + dbs_info->requested_freq = requested_freq;
>
> This will have a side effect when requested_freq is updated before the
> thresholds checks due to the policy_dbs->idle_periods < UINT_MAX
> check.
>
> Shouldn't that be avoided?
I would say we should.
A hardware design I use is running 4.9 kernel where the check does not
exist yet, so there is not a problem.
Anyway, the check policy_dbs->idle_periods < UINT_MAX can change
requested_freq either to requested_freq = policy->min or
requested_freq -= freq_steps;. The first case will not change anything
for us as policy->max=min=cur. The second, however, will force to
update freq which is definitely not expected when limits are set to
min=max. Simply it will not go out here:
if (load < cs_tuners->down_threshold) {
if (requested_freq == policy->min)
goto out; <---
...
}
Am I right here? If so, shouldn't we check explicitly
/*
* If requested_freq is out of range, it is likely that the limits
* changed in the meantime, so fall back to current frequency in that
* case.
*/
if (requested_freq > policy->max || requested_freq < policy->min)
requested_freq = policy->cur;
+/*
+* If the the new limits min,max are equal, there is no point to process further
+*/
+
+if (requested_freq == policy->max && requested_freq == policy->min)
+ goto out;
Thanks,
/Waldek
