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Date: Thu, 13 Feb 2020 17:59:54 +0530
From: Amit Kucheria <amit.kucheria@...durent.com>
To: Thara Gopinath <thara.gopinath@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, ionela.voinescu@....com,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Zhang Rui <rui.zhang@...el.com>, qperret@...gle.com,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Steven Rostedt <rostedt@...dmis.org>,
Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Sudeep Holla <sudeep.holla@....com>,
Juri Lelli <juri.lelli@...hat.com>, corbet@....net,
LKML <linux-kernel@...r.kernel.org>,
Amit Daniel Kachhap <amit.kachhap@...il.com>,
Javi Merino <javi.merino@...nel.org>
Subject: Re: [Patch v9 1/8] sched/pelt: Add support to track thermal pressure
On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath
<thara.gopinath@...aro.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@...aro.org>
> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.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)
> v8->v9:
> - Defined thermal_load_avg to read rq->avg_thermal.load_avg and
> avoid cacheline miss in unsupported cases as per Peter's
> suggestion.
>
> include/trace/events/sched.h | 4 ++++
> init/Kconfig | 4 ++++
> kernel/sched/pelt.c | 31 +++++++++++++++++++++++++++++++
> kernel/sched/pelt.h | 31 +++++++++++++++++++++++++++++++
> kernel/sched/sched.h | 3 +++
> 5 files changed, 73 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 bd9f1fd..055c3bf 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -463,6 +463,10 @@ 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.
Use consistent wording throughout the series - either capped or
decreased capacity.
> + */
This could be shortened to:
Delta capacity of cpu = Actual capacity - Capped 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..916979a 100644
> --- a/kernel/sched/pelt.h
> +++ b/kernel/sched/pelt.h
> @@ -7,6 +7,26 @@ 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);
> +
> +static inline u64 thermal_load_avg(struct rq *rq)
> +{
> + return READ_ONCE(rq->avg_thermal.load_avg);
> +}
> +#else
> +static inline int
> +update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
> +{
> + return 0;
> +}
> +
> +static inline u64 thermal_load_avg(struct rq *rq)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
> int update_irq_load_avg(struct rq *rq, u64 running);
> #else
> @@ -159,6 +179,17 @@ 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 u64 thermal_load_avg(struct rq *rq)
> +{
> + 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 1a88dc8..1f256cb 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -944,6 +944,9 @@ struct rq {
> #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
> struct sched_avg avg_irq;
> #endif
> +#ifdef CONFIG_HAVE_SCHED_THERMAL_PRESSURE
> + struct sched_avg avg_thermal;
> +#endif
> u64 idle_stamp;
> u64 avg_idle;
>
> --
> 2.1.4
>
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