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Date: Thu, 13 Feb 2020 09:11:37 -0500
From: Thara Gopinath <thara.gopinath@...aro.org>
To: Amit Kucheria <amit.kucheria@...durent.com>
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 02/13/2020 07:29 AM, Amit Kucheria wrote:
> 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.
Sure! Will fix it.
>
> It would also help, if you expanded on what you mean by binary in the
> commit description and how the delta capacity is weighted.
I don't understand this. Binary means 0 or 1. delta capacity is time
weighted, i will update this.
>
>> + * 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
Will fix this.
>
>> +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
>>
--
Warm Regards
Thara
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