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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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