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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Thu, 28 Sep 2023 23:26:58 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Lu Jialin <lujialin4@huawei.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] psi: update psi irqtime when the irq delta is nozero
Message-ID: <ZRXvoq6uNk4+cs7Q@gmail.com>
References: <20230810131514.910401-1-lujialin4@huawei.com>
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* Lu Jialin <lujialin4@huawei.com> wrote:

> If update psi irqtime whether the irq delta is zero or not, the performance
> will be degradation when update_rq_clock_task works frequently.
> Therefore, just update psi irqtime whether the irq delta is nozero.
> performace test of times(libmicro):
> 1) without psi_account_irqtime in update_rq_clock_task
> [root@arm64_perf]# ./times  -E -C 200 -L -S -W -N "times" -I 200
> Running: times# ./../bin-arm64/times -E -C 200 -L -S -W -N times -I 200
>              prc thr   usecs/call      samples   errors cnt/samp
> times          1   1      0.45210          188        0      500
> 
> 2) psi_account_irqtime in update_rq_clock_task
> [root@arm64_perf]# ./times  -E -C 200 -L -S -W -N "times" -I 200
> Running: times# ./../bin-arm64/times -E -C 200 -L -S -W -N times -I 200
>              prc thr   usecs/call      samples   errors cnt/samp
> times          1   1      0.49408          196        0      500
> 
> 3) psi_account_irqtime in update_rq_clock_task when irq delta is nozero
> [root@arm64_perf]# ./times  -E -C 200 -L -S -W -N "times" -I 200
> Running: times# ./../bin-arm64/times -E -C 200 -L -S -W -N times -I 200
>              prc thr   usecs/call      samples   errors cnt/samp
> times          1   1      0.45158          195        0      500
> 
> Signed-off-by: Lu Jialin <lujialin4@huawei.com>
> ---
>  kernel/sched/core.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c52c2eba7c73..69c4f229d6d1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -722,7 +722,8 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
>  
>  	rq->prev_irq_time += irq_delta;
>  	delta -= irq_delta;
> -	psi_account_irqtime(rq->curr, irq_delta);
> +	if (irq_delta)
> +		psi_account_irqtime(rq->curr, irq_delta);
>  	delayacct_irq(rq->curr, irq_delta);

Erm, if irq_delta is zero, then a whole bunch of code around the place you
modified becomes NOP as well, right?

Thanks,

	Ingo