linux-kernel - Re: [PATCH 1/9] sched/psi: fix periodic aggregation shut off

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Message-ID: <Yt65LEyN83mTGxwF@cmpxchg.org>
Date:   Mon, 25 Jul 2022 11:39:24 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     surenb@...gle.com, mingo@...hat.com, peterz@...radead.org,
        tj@...nel.org, corbet@....net, akpm@...ux-foundation.org,
        rdunlap@...radead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, songmuchun@...edance.com,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 1/9] sched/psi: fix periodic aggregation shut off

On Thu, Jul 21, 2022 at 12:04:31PM +0800, Chengming Zhou wrote:
> @@ -871,13 +861,23 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
>  				clear |= TSK_MEMSTALL_RUNNING;
>  			if (prev->in_iowait)
>  				set |= TSK_IOWAIT;
> +
> +			/*
> +			 * Periodic aggregation shuts off if there is a period of no
> +			 * task changes, so we wake it back up if necessary. However,
> +			 * don't do this if the task change is the aggregation worker
> +			 * itself going to sleep, or we'll ping-pong forever.
> +			 */
> +			if (unlikely((prev->flags & PF_WQ_WORKER) &&
> +				     wq_worker_last_func(prev) == psi_avgs_work))
> +				wake_clock = false;
>  		}
>  
>  		psi_flags_change(prev, clear, set);
>  
>  		iter = NULL;
>  		while ((group = iterate_groups(prev, &iter)) && group != common)
> -			psi_group_change(group, cpu, clear, set, now, true);
> +			psi_group_change(group, cpu, clear, set, now, wake_clock);
>  
>  		/*
>  		 * TSK_ONCPU is handled up to the common ancestor. If we're tasked

Wait, there is another psi_group_change() below this, which handles
the clearing of TSK_RUNNING for common ancestors. We don't want to
wake those either, so it needs s/true/wake_clock/ as well.