linux-kernel - Re: [RESEND][PATCH v2 3/3] schedutil: trace: Add tracing to capture filter out requests

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Message-ID: <20230531183105.r5tqpdx5axoogkzp@airbuntu>
Date:   Wed, 31 May 2023 19:31:05 +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,
        rafael@...nel.org, linux-pm@...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, kernel test robot <lkp@...el.com>
Subject: Re: [RESEND][PATCH v2 3/3] schedutil: trace: Add tracing to capture
 filter out requests

On 05/22/23 15:57, Lukasz Luba wrote:
> Some of the frequency update requests coming form the task scheduler
> might be filter out. It can happen when the previous request was served
> not that long ago (in a period smaller than provided by the cpufreq driver
> as minimum for frequency update). In such case, we want to know if some of
> the frequency updates cannot make through.
> Export the new tracepoint as well. That would allow to handle it by a
> toolkit for trace analyzes.
> 
> Reported-by: kernel test robot <lkp@...el.com> # solved tricky build
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  include/trace/events/sched.h     |  4 ++++
>  kernel/sched/cpufreq_schedutil.c | 10 ++++++++--
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index dbfb30809f15..e34b7cd5de73 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -739,6 +739,10 @@ DECLARE_TRACE(uclamp_update_tsk_tp,
>  	TP_PROTO(struct task_struct *tsk, int uclamp_id,  unsigned int value),
>  	TP_ARGS(tsk, uclamp_id, value));
>  
> +DECLARE_TRACE(schedutil_update_filtered_tp,
> +	TP_PROTO(int cpu),
> +	TP_ARGS(cpu));
> +
>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index f462496e5c07..4f9daf258a65 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -6,6 +6,8 @@
>   * Author: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>   */
>  
> +EXPORT_TRACEPOINT_SYMBOL_GPL(schedutil_update_filtered_tp);
> +
>  #define IOWAIT_BOOST_MIN	(SCHED_CAPACITY_SCALE / 8)
>  
>  struct sugov_tunables {
> @@ -318,8 +320,10 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
>  
>  	ignore_dl_rate_limit(sg_cpu);
>  
> -	if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
> +	if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) {
> +		trace_schedutil_update_filtered_tp(sg_cpu->cpu);
>  		return false;
> +	}

Can't we have something more generic here too? Are you interested to count
these events? How do you plan to use it?

I think this will be a very noisy event by the way.


Thanks

--
Qais Yousef

>  
>  	sugov_get_util(sg_cpu);
>  	sugov_iowait_apply(sg_cpu, time, max_cap);
> @@ -446,8 +450,10 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
>  
>  	ignore_dl_rate_limit(sg_cpu);
>  
> -	if (!sugov_should_update_freq(sg_policy, time))
> +	if (!sugov_should_update_freq(sg_policy, time)) {
> +		trace_schedutil_update_filtered_tp(sg_cpu->cpu);
>  		goto unlock;
> +	}
>  
>  	next_f = sugov_next_freq_shared(sg_cpu, time);
>  
> -- 
> 2.25.1
>