linux-kernel - Re: [PATCH 3/8] sched/eevdf: Fix HRTICK duration

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Message-ID: <a29f9f4f-d86a-47ce-840e-6ed2cd6f14b7@amd.com>
Date: Fri, 19 Sep 2025 21:04:02 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>, <tglx@...utronix.de>
CC: <arnd@...db.de>, <anna-maria@...utronix.de>, <frederic@...nel.org>,
	<luto@...nel.org>, <mingo@...hat.com>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<vschneid@...hat.com>, <linux-kernel@...r.kernel.org>,
	<oliver.sang@...el.com>
Subject: Re: [PATCH 3/8] sched/eevdf: Fix HRTICK duration

Hello Peter,

On 9/18/2025 1:22 PM, Peter Zijlstra wrote:
> +	/*
> +	 * Compute time until virtual deadline
> +	 */
> +	vdelta = se->deadline - se->vruntime;
> +	if ((s64)vdelta < 0) {
> +		if (task_current_donor(rq, p))
> +			resched_curr(rq);

Why the task_current_donor() check? If the scheduling context has run
out of gas, shouldn't we reschedule curr even if we were proxied?

> +		return;
> +	}
> +	delta = (se->load.weight * vdelta) / NICE_0_LOAD;
> +
> +	/*
> +	 * Correct for instantaneous load of other classes.
> +	 */
> +	util += cpu_util_dl(rq);
> +	util += cpu_util_rt(rq);
> +	util += cpu_util_irq(rq);
> +	if (util && util < 1024) {
> +		scale *= 1024;
> +		scale /= (1024 - util);
>  	}

Could it be possible that we arrive here from the dl_server's pick and
end up inflating the HRTICK duration despite having an uninterrupted
period for fair tasks ahead?

> +
> +	hrtick_start(rq, (scale * delta) / 1024);
>  }
>  
>  /*
-- 
Thanks and Regards,
Prateek