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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Breno Leitao <leitao@debian.org>
Cc: Hillf Danton <hdanton@sina.com>, Tejun Heo <tj@kernel.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org, marco.crivellari@suse.com,
	frederic@kernel.org
Subject: Re: [PATCH 2/2] workqueue: defer wake_up_process() outside
 pool->lock on hot paths
Message-ID: <20260527153500.ERVl3my3@linutronix.de>
References: <20260526-fastwake-v1-0-e69ad86923e6@debian.org>
 <20260526212346.1100-1-hdanton@sina.com>
 <aha6ENW-K-4F4AHi@gmail.com>
 <ahcEcR6ApWr7E4ID@gmail.com>
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In-Reply-To: <ahcEcR6ApWr7E4ID@gmail.com>

On 2026-05-27 07:51:17 [-0700], Breno Leitao wrote:
> @@ -3447,7 +3459,13 @@ static int worker_thread(void *__worker)
>  		return 0;
>  	}
>  
> -	worker_leave_idle(worker);
> +	/*
> +	 * Kicked workers have already been removed from pool->idle_list
> +	 * by kick_pool(); only first-time wakeups (via create_worker())
> +	 * still arrive with WORKER_IDLE set.
> +	 */
> +	if (worker->flags & WORKER_IDLE)
> +		worker_leave_idle(worker);

Couldn't create_worker() be aligned here not set the idle flag and wake
the thread a few lines later? Then we wouldn't have to conditionally
clear the idle flag here (which sort of NULL renders the flag check in
worker_leave_idle()).

>  recheck:
>  	/* no more worker necessary? */
>  	if (!need_more_worker(pool))

Sebastian