linux-kernel - Re: [PATCH linux-next 2/3] sched/psi: Avoid update triggers and rtpoll

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Date:   Mon, 9 Oct 2023 14:52:02 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     yang.yang29@....com.cn
Cc:     surenb@...gle.com, peterz@...radead.org, hannes@...xchg.org,
        mingo@...hat.com, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com
Subject: Re: [PATCH linux-next 2/3] sched/psi: Avoid update triggers and
 rtpoll_total when it is unnecessary


* yang.yang29@....com.cn <yang.yang29@....com.cn> wrote:

> From: Yang Yang <yang.yang29@....com.cn>
> 
> When psimon wakes up and there are no state changes for rtpoll_states,
> it's unnecessary to update triggers and rtpoll_total because the pressures
> being monitored by user had not changed. This will help to slightly reduce
> unnecessary computations of psi.
> 
> And update group->rtpoll_next_update after called update_triggers() and
> update rtpoll_total. This will prevent bugs if update_triggers() uses
> group->rtpoll_next_update in the future, and it makes more sense
> to set the next update time after we finished the current update.

>  	if (now >= group->rtpoll_next_update) {
> -		update_triggers(group, now, &update_total, PSI_POLL);
> -		group->rtpoll_next_update = now + group->rtpoll_min_period;
> -		if (update_total)
> +		if (changed_states & group->rtpoll_states) {
> +			update_triggers(group, now, &update_total, PSI_POLL);
>  			memcpy(group->rtpoll_total, group->total[PSI_POLL],
>  				   sizeof(group->rtpoll_total));
> +		}
> +		group->rtpoll_next_update = now + group->rtpoll_min_period;

So please also split out the second change into a separate patch as well, 
as it's an unrelated patch to the state-change optimization.

We have a "one conceptual change per patch" rule for most things.

Thanks,

	Ingo