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SubjectRe: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure
On Thu, Feb 13, 2020 at 5:33 PM Amit Kucheria <amit.kucheria@linaro.org> wrote:
>
> On Wed, Jan 15, 2020 at 1:27 AM Thara Gopinath
> <thara.gopinath@linaro.org> wrote:
> >
> > Extrapolating on the existing framework to track rt/dl utilization using
> > pelt signals, add a similar mechanism to track thermal pressure. The
> > difference here from rt/dl utilization tracking is that, instead of
> > tracking time spent by a cpu running a rt/dl task through util_avg, the
> > average thermal pressure is tracked through load_avg. This is because
> > thermal pressure signal is weighted "delta" capacity and is not
> > binary(util_avg is binary). "delta capacity" here means delta between the
> > actual capacity of a cpu and the decreased capacity a cpu due to a thermal
> > event.
> >
> > In order to track average thermal pressure, a new sched_avg variable
> > avg_thermal is introduced. Function update_thermal_load_avg can be called
> > to do the periodic bookkeeping (accumulate, decay and average) of the
> > thermal pressure.
> >
> > Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> > ---
> >
> > v6->v7:
> > - Added CONFIG_HAVE_SCHED_THERMAL_PRESSURE to stub out
> > update_thermal_load_avg in unsupported architectures as per
> > review comments from Peter, Dietmar and Quentin.
> > - Updated comment for update_thermal_load_avg as per review
> > comments from Peter and Dietmar.
> > v7->v8:
> > - Fixed typo in defining update_thermal_load_avg which was
> > causing build errors (reported by kbuild test report)
> >
> > include/trace/events/sched.h | 4 ++++
> > init/Kconfig | 4 ++++
> > kernel/sched/pelt.c | 31 +++++++++++++++++++++++++++++++
> > kernel/sched/pelt.h | 16 ++++++++++++++++
> > kernel/sched/sched.h | 1 +
> > 5 files changed, 56 insertions(+)
> >
> > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> > index 420e80e..a8fb667 100644
> > --- a/include/trace/events/sched.h
> > +++ b/include/trace/events/sched.h
> > @@ -613,6 +613,10 @@ DECLARE_TRACE(pelt_dl_tp,
> > TP_PROTO(struct rq *rq),
> > TP_ARGS(rq));
> >
> > +DECLARE_TRACE(pelt_thermal_tp,
> > + TP_PROTO(struct rq *rq),
> > + TP_ARGS(rq));
> > +
> > DECLARE_TRACE(pelt_irq_tp,
> > TP_PROTO(struct rq *rq),
> > TP_ARGS(rq));
> > diff --git a/init/Kconfig b/init/Kconfig
> > index f6a4a91..c16ea88 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -450,6 +450,10 @@ config HAVE_SCHED_AVG_IRQ
> > depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
> > depends on SMP
> >
> > +config HAVE_SCHED_THERMAL_PRESSURE
> > + bool "Enable periodic averaging of thermal pressure"
> > + depends on SMP
> > +
> > config BSD_PROCESS_ACCT
> > bool "BSD Process Accounting"
> > depends on MULTIUSER
> > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> > index bd006b7..5d1fbf0 100644
> > --- a/kernel/sched/pelt.c
> > +++ b/kernel/sched/pelt.c
> > @@ -367,6 +367,37 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
> > return 0;
> > }
> >
> > +#ifdef CONFIG_HAVE_SCHED_THERMAL_PRESSURE
> > +/*
> > + * thermal:
> > + *
> > + * load_sum = \Sum se->avg.load_sum but se->avg.load_sum is not tracked
> > + *
> > + * util_avg and runnable_load_avg are not supported and meaningless.
> > + *
> > + * Unlike rt/dl utilization tracking that track time spent by a cpu
> > + * running a rt/dl task through util_avg, the average thermal pressure is
> > + * tracked through load_avg. This is because thermal pressure signal is
> > + * weighted "delta" capacity and is not binary(util_avg is binary). "delta
>
> May I suggest a slight rewording here and in the commit description,
>
> This is because the thermal pressure signal is weighted "delta"
> capacity unlike util_avg which is binary.
>
> It would also help, if you expanded on what you mean by binary in the
> commit description and how the delta capacity is weighted.
>
> > + * capacity" here means delta between the actual capacity of a cpu and the
> > + * decreased capacity a cpu due to a thermal event.
>
> This could be shortened to:
>
> Delta capacity of cpu = Actual capacity - Decreased capacity due to
> thermal event
>

Please ignore. I should have sent this against v9, it was languishing
in my mailbox since v8 and I sent this out by mistake.

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