linux-kernel - Re: [PATCH 1/3] sched/tp: Add new tracepoint to track uclamp set from user-space

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Date:   Mon, 3 Apr 2023 14:46:06 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        rostedt@...dmis.org, mhiramat@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, delyank@...com, qyousef@...gle.com
Subject: Re: [PATCH 1/3] sched/tp: Add new tracepoint to track uclamp set
 from user-space

Hi Lukasz!

On 03/22/23 15:18, Lukasz Luba wrote:
> The user-space can set uclamp value for a given task. It impacts task
> placement decisions made by the scheduler. This is very useful information
> and helps to understand the system behavior or track improvements in
> middleware and applications which start using uclamp mechanisms and report
> better performance in tests.

We do have uclamp trace events in sched_tp, why are they not sufficient?

	https://github.com/qais-yousef/sched_tp/blob/main/sched_events.h#L233

Do you really want to know the exact time the value has changed?

Would it make sense to introduce a generic sched_setscheduler tracepoint
instead? Although this might not be necessary as I think we can use
register_kprobe() to register a callback and create a new event without any
additional tracepoint. sched_setscheduler() is not inlined so should be easy to
hook into and create events, no?


Thanks

--
Qais Yousef

> 
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  include/trace/events/sched.h | 4 ++++
>  kernel/sched/core.c          | 5 +++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index fbb99a61f714..dbfb30809f15 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -735,6 +735,10 @@ DECLARE_TRACE(sched_update_nr_running_tp,
>  	TP_PROTO(struct rq *rq, int change),
>  	TP_ARGS(rq, change));
>  
> +DECLARE_TRACE(uclamp_update_tsk_tp,
> +	TP_PROTO(struct task_struct *tsk, int uclamp_id,  unsigned int value),
> +	TP_ARGS(tsk, uclamp_id, value));
> +
>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 488655f2319f..882c92e3ccf0 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -110,6 +110,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(uclamp_update_tsk_tp);
>  
>  DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
>  
> @@ -1936,12 +1937,16 @@ static void __setscheduler_uclamp(struct task_struct *p,
>  	    attr->sched_util_min != -1) {
>  		uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
>  			      attr->sched_util_min, true);
> +		trace_uclamp_update_tsk_tp(p, UCLAMP_MIN,
> +					   attr->sched_util_min);
>  	}
>  
>  	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
>  	    attr->sched_util_max != -1) {
>  		uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
>  			      attr->sched_util_max, true);
> +		trace_uclamp_update_tsk_tp(p, UCLAMP_MAX,
> +					   attr->sched_util_max);
>  	}
>  }
>  
> -- 
> 2.17.1
>