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    SubjectRe: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure
    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

    > + */
    > +
    > +int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
    > +{
    > + if (___update_load_sum(now, &rq->avg_thermal,
    > + capacity,
    > + capacity,
    > + capacity)) {
    > + ___update_load_avg(&rq->avg_thermal, 1, 1);
    > + trace_pelt_thermal_tp(rq);
    > + return 1;
    > + }
    > +
    > + return 0;
    > +}
    > +#endif
    > +
    > #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
    > /*
    > * irq:
    > diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h
    > index afff644..bf1e17b 100644
    > --- a/kernel/sched/pelt.h
    > +++ b/kernel/sched/pelt.h
    > @@ -7,6 +7,16 @@ int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq);
    > int update_rt_rq_load_avg(u64 now, struct rq *rq, int running);
    > int update_dl_rq_load_avg(u64 now, struct rq *rq, int running);
    >
    > +#ifdef CONFIG_HAVE_SCHED_THERMAL_PRESSURE
    > +int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity);
    > +#else
    > +static inline int
    > +update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
    > +{
    > + return 0;
    > +}
    > +#endif
    > +
    > #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
    > int update_irq_load_avg(struct rq *rq, u64 running);
    > #else
    > @@ -159,6 +169,12 @@ update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
    > }
    >
    > static inline int
    > +update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
    > +{
    > + return 0;
    > +}
    > +
    > +static inline int
    > update_irq_load_avg(struct rq *rq, u64 running)
    > {
    > return 0;
    > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    > index 280a3c7..37bd7ef 100644
    > --- a/kernel/sched/sched.h
    > +++ b/kernel/sched/sched.h
    > @@ -944,6 +944,7 @@ struct rq {
    > #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
    > struct sched_avg avg_irq;
    > #endif
    > + struct sched_avg avg_thermal;
    > u64 idle_stamp;
    > u64 avg_idle;
    >
    > --
    > 2.1.4
    >

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