Re: [PATCH v2 2/2] sched: Make iowait_boost optional in schedutil

[Saravana Kannan]

On 05/19/2017 09:10 AM, Joel Fernandes wrote:
> Hi Viresh,
>
> On Thu, May 18, 2017 at 11:50 PM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> > On 18-05-17, 23:23, Joel Fernandes wrote:
> > > We should apply the iowait boost only if cpufreq policy has iowait boost
> > > enabled. Also make it a schedutil configuration from sysfs so it can be turned
> > > on/off if needed (by default initialize it to the policy value).
> > >
> > > For systems that don't need/want it enabled, such as those on arm64 based
> > > mobile devices that are battery operated, it saves energy when the cpufreq
> > > driver policy doesn't have it enabled (details below):
> > >
> > > Here are some results for energy measurements collected running a YouTube video
> > > for 30 seconds:
> > > Before: 8.042533 mWh
> > > After: 7.948377 mWh
> > > Energy savings is ~1.2%
> > >
> > > Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> > > Cc: Len Brown <lenb@xxxxxxxxxx>
> > > Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> > > Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
> > > ---
> > >   kernel/sched/cpufreq_schedutil.c | 32 ++++++++++++++++++++++++++++++++
> > >   1 file changed, 32 insertions(+)
> > >
> > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > > index 76877a62b5fa..0e392b58b9b3 100644
> > > --- a/kernel/sched/cpufreq_schedutil.c
> > > +++ b/kernel/sched/cpufreq_schedutil.c
> > > @@ -24,6 +24,7 @@
> > >   struct sugov_tunables {
> > >        struct gov_attr_set attr_set;
> > >        unsigned int rate_limit_us;
> > > +     bool iowait_boost_enable;
> >
> > I suggested s/iowait_boost_enable/iowait_boost/ and you said okay for
> > that change.
>
> Yes, I somehow only picked up 'bool' from your comment.  I'll drop the
> '_enable' in the next version. Sorry and thanks.
>
> > >   };
> > >
> > >   struct sugov_policy {
> > > @@ -171,6 +172,11 @@ static void sugov_get_util(unsigned long *util, unsigned long *max)
> > >   static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> > >                                   unsigned int flags)
> > >   {
> > > +     struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> > > +
> > > +     if (!sg_policy->tunables->iowait_boost_enable)
> > > +             return;
> > > +
> > >        if (flags & SCHED_CPUFREQ_IOWAIT) {
> > >                sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
> > >        } else if (sg_cpu->iowait_boost) {
> > > @@ -386,10 +392,34 @@ static ssize_t rate_limit_us_store(struct gov_attr_set *attr_set, const char *bu
> > >        return count;
> > >   }
> > >
> > > +static ssize_t iowait_boost_enable_show(struct gov_attr_set *attr_set,
> > > +                                     char *buf)
> > > +{
> > > +     struct sugov_tunables *tunables = to_sugov_tunables(attr_set);
> > > +
> > > +     return sprintf(buf, "%u\n", tunables->iowait_boost_enable);
> > > +}
> > > +
> > > +static ssize_t iowait_boost_enable_store(struct gov_attr_set *attr_set,
> > > +                                      const char *buf, size_t count)
> > > +{
> > > +     struct sugov_tunables *tunables = to_sugov_tunables(attr_set);
> > > +     bool enable;
> > > +
> > > +     if (kstrtobool(buf, &enable))
> > > +             return -EINVAL;
> > > +
> > > +     tunables->iowait_boost_enable = enable;
> > > +
> > > +     return count;
> > > +}
> > > +
> > >   static struct governor_attr rate_limit_us = __ATTR_RW(rate_limit_us);
> > > +static struct governor_attr iowait_boost_enable = __ATTR_RW(iowait_boost_enable);
> > >
> > >   static struct attribute *sugov_attributes[] = {
> > >        &rate_limit_us.attr,
> > > +     &iowait_boost_enable.attr,
> > >        NULL
> > >   };
> >
> > Do we really need this right now? I mean, are you going to use it this
> > way? It may never get used eventually and may be better to leave the
> > sysfs option for now.
>
> I felt it is good to leave it to the system designer and have the
> policy set a 'default' value, so incase it isn't touched by the
> designer from userspace, then the policy default is fine, and if the
> designer chooses to change it then he has the option to. This is also
> how we currently set the rate limits for schedutil in android. I don't
> feel strongly about one way or the other and if the general consensus
> is to drop this part then I'm fine. I'm curious to know what others
> think as well though.

Acked-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>



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