Re: [PATCH v3 5/6] sched: Add sched_overutilized tracepoint

From: Peter Zijlstra <peterz@infradead.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org,
	Pavankumar Kondeti <pkondeti@codeaurora.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Uwe Kleine-Konig <u.kleine-koenig@pengutronix.de>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Quentin Perret <quentin.perret@arm.com>
Subject: Re: [PATCH v3 5/6] sched: Add sched_overutilized tracepoint
Date: Mon, 17 Jun 2019 17:50:10 +0200	[thread overview]
Message-ID: <20190617155010.GH3436@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190604111459.2862-6-qais.yousef@arm.com>

On Tue, Jun 04, 2019 at 12:14:58PM +0100, Qais Yousef wrote:
> The new tracepoint allows us to track the changes in overutilized
> status.
> 
> Overutilized status is associated with EAS. It indicates that the system
> is in high performance state. EAS is disabled when the system is in this
> state since there's not much energy savings while high performance tasks
> are pushing the system to the limit and it's better to default to the
> spreading behavior of the scheduler.
> 
> This tracepoint helps understanding and debugging the conditions under
> which this happens.
> 
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> ---
>  include/trace/events/sched.h |  4 ++++
>  kernel/sched/fair.c          | 11 +++++++++--
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index c7dd9bc7f001..edd96e04049f 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -621,6 +621,10 @@ DECLARE_TRACE(pelt_se_tp,
>  	TP_PROTO(struct sched_entity *se),
>  	TP_ARGS(se));
>  
> +DECLARE_TRACE(sched_overutilized_tp,
> +	TP_PROTO(int overutilized, struct root_domain *rd),
> +	TP_ARGS(overutilized, rd));
> +

strictly speaking you only need @rd :-)

>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8e0015ebf109..e2418741608e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5179,8 +5179,10 @@ static inline bool cpu_overutilized(int cpu)
>  
>  static inline void update_overutilized_status(struct rq *rq)
>  {
> -	if (!READ_ONCE(rq->rd->overutilized) && cpu_overutilized(rq->cpu))
> +	if (!READ_ONCE(rq->rd->overutilized) && cpu_overutilized(rq->cpu)) {
>  		WRITE_ONCE(rq->rd->overutilized, SG_OVERUTILIZED);
> +		trace_sched_overutilized_tp(1, rq->rd);
> +	}
>  }
>  #else
>  static inline void update_overutilized_status(struct rq *rq) { }
> @@ -8542,8 +8544,13 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>  
>  		/* Update over-utilization (tipping point, U >= 0) indicator */
>  		WRITE_ONCE(rd->overutilized, sg_status & SG_OVERUTILIZED);
> +
> +		trace_sched_overutilized_tp(!!(sg_status & SG_OVERUTILIZED), rd);
>  	} else if (sg_status & SG_OVERUTILIZED) {
> -		WRITE_ONCE(env->dst_rq->rd->overutilized, SG_OVERUTILIZED);
> +		struct root_domain *rd = env->dst_rq->rd;
> +
> +		WRITE_ONCE(rd->overutilized, SG_OVERUTILIZED);
> +		trace_sched_overutilized_tp(1, rd);
>  	}
>  }

But I figure since we need both values anyway, this isn't too much of a
bother.

I'm going to flip the argument order though.