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Date: Wed, 27 May 2026 17:22:05 +0200
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Breno Leitao <leitao@debian.org>
Cc: Tejun Heo <tj@kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org, marco.crivellari@suse.com,
	frederic@kernel.org, kernel-team@meta.com
Subject: Re: [PATCH 2/2] workqueue: defer wake_up_process() outside
 pool->lock on hot paths
Message-ID: <20260527152205.OjEsPVjM@linutronix.de>
References: <20260526-fastwake-v1-0-e69ad86923e6@debian.org>
 <20260526-fastwake-v1-2-e69ad86923e6@debian.org>
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In-Reply-To: <20260526-fastwake-v1-2-e69ad86923e6@debian.org>

On 2026-05-26 14:08:06 [-0400], Breno Leitao wrote:
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2423,6 +2424,15 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
>  
>  out:
>  	raw_spin_unlock(&pool->lock);
> +	/*
> +	 * Issue the wakeup after dropping pool->lock to shorten the
> +	 * locked region on this hot enqueue path.  kick_pool_pick() did all
> +	 * of the work that required the lock (worker selection and
> +	 * wake_cpu setup); the wake_up_process() itself only needs to
> +	 * take the target rq->lock.
> +	 */
> +	if (wake_p)
> +		wake_up_process(wake_p);

What about using wake_q_add() to grab a worker(s) and then wake_up_q()
to wake the worker outside of the lock?

>  	rcu_read_unlock();
>  }
>  

Sebastian