linux-kernel - Re: [PATCH 2/8] sched/fair: Limit hrtick work

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Message-ID: <ce1243d6-365b-42e5-b8da-7eb821d6f4a2@amd.com>
Date: Fri, 19 Sep 2025 20:29:09 +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 2/8] sched/fair: Limit hrtick work

Hello Peter,

On 9/18/2025 1:22 PM, Peter Zijlstra wrote:
> @@ -13119,6 +13119,12 @@ static void task_tick_fair(struct rq *rq
>  		entity_tick(cfs_rq, se, queued);
>  	}
>  
> +	if (queued) {
> +		if (!need_resched())
> +			hrtick_start_fair(rq, curr);

Do we need a hrtick_start_fair() here? Queued tick will always do a
resched_curr_lazy() - if another HRTICK fires before the next tick,
all it'll do is resched_curr_lazy() again and the next opportunity to
resched is either exit to userspace or the periodic tick firing and
promoting that LAZY to a full NEED_RESCHED.

The early return does makes sense.

> +		return;
> +	}
> +
>  	if (static_branch_unlikely(&sched_numa_balancing))
>  		task_tick_numa(rq, curr);
>  

-- 
Thanks and Regards,
Prateek