On Thu, May 19, 2016 at 01:37:40AM +0200, Rafael J. Wysocki wrote:
> On Mon, May 9, 2016 at 11:20 PM, Steve Muckle <steve.muc...@linaro.org> wrote:
> > The mechanisms for remote CPU updates and slow-path frequency
> > transitions are relatively expensive - the former is an IPI while the
> > latter requires waking up a thread to do work. These activities should
> > be avoided if they are not necessary. To that end, calculate the
> > actual target-supported frequency required by the new utilization
> > value in schedutil. If it is the same as the previously requested
> > frequency then there is no need to continue with the update.
>
> Unless the max/min limits changed in the meantime, right?
Right, I'll amend the commit text. The functionality is correct AFAICS.
> >
> > Signed-off-by: Steve Muckle <smuc...@linaro.org>
> > ---
> > kernel/sched/cpufreq_schedutil.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c
> > b/kernel/sched/cpufreq_schedutil.c
> > index 6cb2ecc204ec..e185075fcb5c 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -153,14 +153,26 @@ static void sugov_update_commit(struct sugov_cpu
> > *sg_cpu, int cpu, u64 time,
> > * next_freq = C * curr_freq * util_raw / max
> > *
> > * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8.
> > + *
> > + * The lowest target-supported frequency which is equal or greater than
> > the raw
> > + * next_freq (as calculated above) is returned, or the CPU's max_freq if
> > such
> > + * a target-supported frequency does not exist.
> > */
> > static unsigned int get_next_freq(struct cpufreq_policy *policy,
> > unsigned long util, unsigned long max)
> > {
> > + struct cpufreq_frequency_table *entry;
> > unsigned int freq = arch_scale_freq_invariant() ?
> > policy->cpuinfo.max_freq : policy->cur;
> > + unsigned int target_freq = UINT_MAX;
> > +
> > + freq = (freq + (freq >> 2)) * util / max;
> > +
> > + cpufreq_for_each_valid_entry(entry, policy->freq_table)
> > + if (entry->frequency >= freq && entry->frequency <
> > target_freq)
> > + target_freq = entry->frequency;
>
> Please don't assume that every driver will have a frequency table.
> That may not be the case in the future (and I'm not even sure about
> the existing CPPC driver for that matter).
For platforms without a frequency table I guess we can just continue
with the current behavior, passing in the raw calculated frequency. I'll
make this change.
At some point I imagine those platforms will want to somehow achieve
similar behavior to avoid very small transitions that do not result in
real benefit. Maybe some sort of threshold % in the schedutil down the
road.
thanks,
Steve
