linux-kernel - Re: [PATCH v4 5/5] sched/pelt: Remove shift of thermal clock

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Date: Tue, 30 Jan 2024 00:36:35 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
	sudeep.holla@....com, rafael@...nel.org, viresh.kumar@...aro.org,
	agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
	mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	lukasz.luba@....com, rui.zhang@...el.com, mhiramat@...nel.org,
	daniel.lezcano@...aro.org, amit.kachhap@...il.com, corbet@....net,
	gregkh@...uxfoundation.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 5/5] sched/pelt: Remove shift of thermal clock

On 01/09/24 17:46, Vincent Guittot wrote:
> The optional shift of the clock used by thermal/hw load avg has been
> introduced to handle case where the signal was not always a high frequency
> hw signal. Now that cpufreq provides a signal for firmware and
> SW pressure, we can remove this exception and always keep this PELT signal
> aligned with other signals.
> Mark sysctl_sched_migration_cost boot parameter as deprecated
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---

Better without it, yes.

Reviewed-by: Qais Yousef <qyousef@...alina.io>

>  .../admin-guide/kernel-parameters.txt          |  1 +
>  kernel/sched/core.c                            |  2 +-
>  kernel/sched/fair.c                            | 10 ++--------
>  kernel/sched/sched.h                           | 18 ------------------
>  4 files changed, 4 insertions(+), 27 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 65731b060e3f..2ee15522b15d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5722,6 +5722,7 @@
>  			but is useful for debugging and performance tuning.
>  
>  	sched_thermal_decay_shift=
> +			[Deprecated]
>  			[KNL, SMP] Set a decay shift for scheduler thermal
>  			pressure signal. Thermal pressure signal follows the
>  			default decay period of other scheduler pelt
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a6f084bdf1c5..c68e47bfd5ae 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5670,7 +5670,7 @@ void scheduler_tick(void)
>  
>  	update_rq_clock(rq);
>  	hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
> -	update_hw_load_avg(rq_clock_hw(rq), rq, hw_pressure);
> +	update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure);
>  	curr->sched_class->task_tick(rq, curr, 0);
>  	if (sched_feat(LATENCY_WARN))
>  		resched_latency = cpu_resched_latency(rq);
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f1c3d600d6d6..d5ba6cdb141c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -78,15 +78,9 @@ static unsigned int normalized_sysctl_sched_base_slice	= 750000ULL;
>  
>  const_debug unsigned int sysctl_sched_migration_cost	= 500000UL;
>  
> -int sched_hw_decay_shift;
>  static int __init setup_sched_thermal_decay_shift(char *str)
>  {
> -	int _shift = 0;
> -
> -	if (kstrtoint(str, 0, &_shift))
> -		pr_warn("Unable to set scheduler thermal pressure decay shift parameter\n");
> -
> -	sched_hw_decay_shift = clamp(_shift, 0, 10);
> +	pr_warn("Ignoring the deprecated sched_thermal_decay_shift= option\n");
>  	return 1;
>  }
>  __setup("sched_thermal_decay_shift=", setup_sched_thermal_decay_shift);
> @@ -9247,7 +9241,7 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
>  
>  	decayed = update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
>  		  update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
> -		  update_hw_load_avg(rq_clock_hw(rq), rq, hw_pressure) |
> +		  update_hw_load_avg(now, rq, hw_pressure) |
>  		  update_irq_load_avg(rq, 0);
>  
>  	if (others_have_blocked(rq))
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 677d24202eec..6fc6718a1060 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1520,24 +1520,6 @@ static inline u64 rq_clock_task(struct rq *rq)
>  	return rq->clock_task;
>  }
>  
> -/**
> - * By default the decay is the default pelt decay period.
> - * The decay shift can change the decay period in
> - * multiples of 32.
> - *  Decay shift		Decay period(ms)
> - *	0			32
> - *	1			64
> - *	2			128
> - *	3			256
> - *	4			512
> - */
> -extern int sched_hw_decay_shift;
> -
> -static inline u64 rq_clock_hw(struct rq *rq)
> -{
> -	return rq_clock_task(rq) >> sched_hw_decay_shift;
> -}
> -
>  static inline void rq_clock_skip_update(struct rq *rq)
>  {
>  	lockdep_assert_rq_held(rq);
> -- 
> 2.34.1
>