linux-kernel - Re: [PATCH rcu/next 3/3] rcu: Fix late wakeup when flush of bypass cblist happens

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Date:   Fri, 16 Sep 2022 14:51:39 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH rcu/next 3/3] rcu: Fix late wakeup when flush of bypass
 cblist happens

On Thu, Sep 15, 2022 at 12:14:19AM +0000, Joel Fernandes (Google) wrote:
> When the bypass cblist gets too big or its timeout has occurred, it is
> flushed into the main cblist. However, the bypass timer is still running
> and the behavior is that it would eventually expire and wake the GP
> thread.
> 
> Since we are going to use the bypass cblist for lazy CBs, do the wakeup
> soon as the flush happens. Otherwise, the lazy-timer will go off much
> later and the now-non-lazy cblist CBs can get stranded for the duration
> of the timer.
> 
> This is a good thing to do anyway, since it makes the behavior consistent with
> behavior of other code paths where queueing something into the ->cblist makes
> the GP kthread in a non-sleeping state quickly.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>