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

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Message-ID: <d75fd0b2-f6e0-4102-a5d2-11c7c5487949@paulmck-laptop>
Date: Fri, 8 Mar 2024 13:52:05 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Uladzislau Rezki <urezki@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>, linux-kernel@...r.kernel.org,
	frederic@...nel.org, boqun.feng@...il.com, neeraj.iitr10@...il.com,
	rcu@...r.kernel.org, rostedt@...dmis.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 Fri, Mar 08, 2024 at 06:38:37PM +0100, Uladzislau Rezki wrote:
> On Fri, Mar 08, 2024 at 04:05:15PM +0100, Uladzislau Rezki wrote:
> > On Thu, Mar 07, 2024 at 04:06:06PM -0800, Paul E. McKenney wrote:
> > > On Thu, Mar 07, 2024 at 06:52:14PM -0500, Joel Fernandes wrote:
> > > > 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.
> > > 
> > > Very good, thank you!
> > > 
> > > Uladzislau, could you please pull this into the next series you send?
> > > I can then replace your commits in -rcu with the updated series.
> > > 
> > Absolutely. I will go through it and send out the next version!
> > 
> 
> Joel, i sent out the v6: [PATCH v6 0/6] Reduce synchronize_rcu() latency(v6)
> 
> Could you please rework the patch on latest tip once the series i sent is
> settled on Paul's dev?

It is there now.

							Thanx, Paul

> I have not sent your patch because it is not cleanly applied and needs some
> review.
> 
> Thank you in advance!
> 
> --
> Uladzislau Rezki