linux-kernel - Re: [PATCH] psi: fix randomized calculation in record

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Message-ID: <20200403152016.GA69203@cmpxchg.org>
Date:   Fri, 3 Apr 2020 11:20:16 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     peterz@...radead.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Daniel Drake <drake@...lessm.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH] psi: fix randomized calculation in record_times()

On Fri, Apr 03, 2020 at 04:55:25AM -0400, Yafang Shao wrote:
> @@ -690,7 +690,10 @@ static void psi_group_change(struct psi_group *group, int cpu,
>  	 */
>  	write_seqcount_begin(&groupc->seq);
>  
> -	record_times(groupc, cpu, false);
> +	if (groupc->total_tasks)
> +		record_times(groupc, cpu, false);
> +	else
> +		groupc->state_start = cpu_clock(cpu);

This change appears is a no-op. If there are no tasks,
groupc->state_mask is 0, and the only thing record_times() does is

	groupc->state_start = cpu_clock(cpu);

Did you encounter actual problems, or are you just reading the code?