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Date: Tue, 20 Nov 2018 15:53:05 +0000
From: Quentin Perret <quentin.perret@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, rjw@...ysocki.net,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
gregkh@...uxfoundation.org, mingo@...hat.com,
dietmar.eggemann@....com, morten.rasmussen@....com,
chris.redpath@....com, patrick.bellasi@....com,
valentin.schneider@....com, vincent.guittot@...aro.org,
thara.gopinath@...aro.org, tkjos@...gle.com,
joel@...lfernandes.org, smuckle@...gle.com,
adharmap@...eaurora.org, skannan@...eaurora.org,
pkondeti@...eaurora.org, juri.lelli@...hat.com,
edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [PATCH v9 02/15] sched/cpufreq: Prepare schedutil for Energy
Aware Scheduling
On Tuesday 20 Nov 2018 at 16:25:14 (+0100), Peter Zijlstra wrote:
> On Tue, Nov 20, 2018 at 10:16:02AM +0530, Viresh Kumar wrote:
> > On 19-11-18, 14:18, Quentin Perret wrote:
> > > @@ -223,20 +222,33 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> >
> > > - if ((util + cpu_util_dl(rq)) >= max)
> > > - return max;
> > > + if (type == FREQUENCY_UTIL) {
> > > + /*
> > > + * For frequency selection we do not make cpu_util_dl() a
> > > + * permanent part of this sum because we want to use
> > > + * cpu_bw_dl() later on, but we need to check if the
> > > + * CFS+RT+DL sum is saturated (ie. no idle time) such
> > > + * that we select f_max when there is no idle time.
> > > + *
> > > + * NOTE: numerical errors or stop class might cause us
> > > + * to not quite hit saturation when we should --
> > > + * something for later.
> > > + */
> > > +
> > > + if ((util + cpu_util_dl(rq)) >= max)
> > > + return max;
> > > + } else {
> > > + /*
> > > + * OTOH, for energy computation we need the estimated
> > > + * running time, so include util_dl and ignore dl_bw.
> > > + */
> > > + util += cpu_util_dl(rq);
> > > + if (util >= max)
> > > + return max;
> > > + }
> >
> > Maybe write above as:
> >
> > dl_util = cpu_util_dl(rq);
> >
> > if ((util + dl_util) >= max)
> > return max;
> >
> > if (type != FREQUENCY_UTIL)
> > util += dl_util;
> >
> >
> > as both the if/else parts were doing almost the same thing.
>
> A little like so ?
>
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -201,8 +201,8 @@ static unsigned int get_next_freq(struct
> unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
> unsigned long max, enum schedutil_type type)
> {
> + unsigned long dl_util, util, irq;
> struct rq *rq = cpu_rq(cpu);
> - unsigned long util, irq;
>
> if (type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt))
> return max;
> @@ -225,30 +225,26 @@ unsigned long schedutil_freq_util(int cp
> util = util_cfs;
> util += cpu_util_rt(rq);
>
> - if (type == FREQUENCY_UTIL) {
> - /*
> - * For frequency selection we do not make cpu_util_dl() a
> - * permanent part of this sum because we want to use
> - * cpu_bw_dl() later on, but we need to check if the
> - * CFS+RT+DL sum is saturated (ie. no idle time) such
> - * that we select f_max when there is no idle time.
> - *
> - * NOTE: numerical errors or stop class might cause us
> - * to not quite hit saturation when we should --
> - * something for later.
> - */
> -
> - if ((util + cpu_util_dl(rq)) >= max)
> - return max;
> - } else {
> - /*
> - * OTOH, for energy computation we need the estimated
> - * running time, so include util_dl and ignore dl_bw.
> - */
> - util += cpu_util_dl(rq);
> - if (util >= max)
> - return max;
> - }
> + dl_util = cpu_util_dl(rq);
> +
> + /*
> + * NOTE: numerical errors or stop class might cause us to not quite hit
> + * saturation when we should -- something for later.
> + */
> + if (util + dl_util > max)
> + return max;
> +
> + /*
> + * For frequency selection we do not make cpu_util_dl() a permanent
> + * part of this sum because we want to use cpu_bw_dl() later on, but we
> + * need to check if the CFS+RT+DL sum is saturated (ie. no idle time)
> + * such that we select f_max when there is no idle time.
We probably want move that paragraph to the comment above no ? Other
than that, the change LGTM.
> + *
> + * OTOH, for energy computation we need the estimated running time, so
> + * do include util_dl and ignore dl_bw.
> + */
> + if (type == ENERGY_UTIL)
> + util += dl_util;
>
> /*
> * There is still idle time; further improve the number by using the
> @@ -262,21 +258,18 @@ unsigned long schedutil_freq_util(int cp
> util = scale_irq_capacity(util, irq, max);
> util += irq;
>
> - if (type == FREQUENCY_UTIL) {
> - /*
> - * Bandwidth required by DEADLINE must always be granted
> - * while, for FAIR and RT, we use blocked utilization of
> - * IDLE CPUs as a mechanism to gracefully reduce the
> - * frequency when no tasks show up for longer periods of
> - * time.
> - *
> - * Ideally we would like to set bw_dl as min/guaranteed
> - * freq and util + bw_dl as requested freq. However,
> - * cpufreq is not yet ready for such an interface. So,
> - * we only do the latter for now.
> - */
> + /*
> + * Bandwidth required by DEADLINE must always be granted while, for
> + * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
> + * to gracefully reduce the frequency when no tasks show up for longer
> + * periods of time.
> + *
> + * Ideally we would like to set bw_dl as min/guaranteed freq and util +
> + * bw_dl as requested freq. However, cpufreq is not yet ready for such
> + * an interface. So, we only do the latter for now.
> + */
> + if (type == FREQUENCY_UTIL)
> util += cpu_bw_dl(rq);
> - }
>
> return min(max, util);
> }
Thanks,
Quentin
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