linux-kernel - Re: [PATCH] [RFC] rcu/tree: Reduce wake up for synchronize

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Message-ID: <CAEXW_YQ-TZB-1gpxvf7v+QAZhHtzV5waBA1VemtgEwNktSp=ww@mail.gmail.com>
Date: Thu, 7 Mar 2024 18:52:14 -0500
From: Joel Fernandes <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org, frederic@...nel.org, boqun.feng@...il.com, 
	urezki@...il.com, neeraj.iitr10@...il.com, joel@...lfernandes.org, 
	rcu@...r.kernel.org, rostedt@...dmis.org, 
	"Paul E. McKenney" <paulmck@...nel.org>, Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, 
	Josh Triplett <josh@...htriplett.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH] [RFC] rcu/tree: Reduce wake up for synchronize_rcu()
 common case

On Thu, Mar 7, 2024 at 6:48 PM Joel Fernandes (Google)
<joel@...lfernandes.org> wrote:
>
> In the synchronize_rcu() common case, we will have less than
> SR_MAX_USERS_WAKE_FROM_GP number of users per GP. Waking up the kworker
> is pointless just to free the last injected wait head since at that point,
> all the users have already been awakened.
>
> Introduce a new counter to track this and prevent the wakeup in the
> common case.
>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---

Forgot to mention, this is based on the latest RCU -dev branch and
passes light rcutorture testing on all configs. Heavier rcutorture
testing (60 minutes) was performed on TREE03.

Thanks.