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Date:   Wed, 7 Dec 2022 18:00:32 +0100
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From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH v2 06/22] sched/fair: Collect load-balancing stats for IPC
 classes
To:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Ricardo Neri <ricardo.neri@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Valentin Schneider <vschneid@redhat.com>, x86@kernel.org,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        "Tim C . Chen" <tim.c.chen@intel.com>
References: <20221128132100.30253-1-ricardo.neri-calderon@linux.intel.com>
 <20221128132100.30253-7-ricardo.neri-calderon@linux.intel.com>
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On 28/11/2022 14:20, Ricardo Neri wrote:

[...]

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 224107278471..3a1d6c50a19b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9100,6 +9100,57 @@ group_type group_classify(unsigned int imbalance_pct,
>  	return group_has_spare;
>  }
>  
> +struct sg_lb_ipcc_stats {
> +	int min_score;	/* Min(score(rq->curr->ipcc)) */
> +	int min_ipcc;	/* Min(rq->curr->ipcc) */
> +	long sum_score; /* Sum(score(rq->curr->ipcc)) */
> +};

Wouldn't it be cleaner to put `min_score`, `min_ipcc` and `sum_score`
into `struct sg_lb_stats` next to `ipcc_score_{after, before}` under the
same #ifdef CONFIG_IPC_CLASSES?

Looks like those IPCC stats would only be needed in the specific
condition under which update_sg_lb_stats_scores() is called?

> +#ifdef CONFIG_IPC_CLASSES
> +static void init_rq_ipcc_stats(struct sg_lb_ipcc_stats *sgcs)
> +{
> +	*sgcs = (struct sg_lb_ipcc_stats) {
> +		.min_score = INT_MAX,
> +	};
> +}
> +
> +/** Called only if cpu_of(@rq) is not idle and has tasks running. */
> +static void update_sg_lb_ipcc_stats(struct sg_lb_ipcc_stats *sgcs,
> +				    struct rq *rq)
> +{
> +	struct task_struct *curr;
> +	unsigned short ipcc;
> +	int score;
> +
> +	if (!sched_ipcc_enabled())
> +		return;
> +
> +	curr = rcu_dereference(rq->curr);
> +	if (!curr || (curr->flags & PF_EXITING) || is_idle_task(curr))

So the Idle task is excluded but RT, DL, (Stopper) tasks are not. Looks
weird if non-CFS tasks could influence CFS load-balancing.
AFAICS, RT and DL tasks could have p->ipcc != IPC_CLASS_UNCLASSIFIED?

[...]