From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: boqun.feng@gmail.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: One potential issue with concurrent execution of RCU callbacks...
Date: Tue, 8 Dec 2020 23:04:38 +0100 [thread overview]
Message-ID: <20201208220438.GC3916@lothringen> (raw)
In-Reply-To: <20201208182409.GT2657@paulmck-ThinkPad-P72>
On Tue, Dec 08, 2020 at 10:24:09AM -0800, Paul E. McKenney wrote:
> > It reduces the code scope running with BH disabled.
> > Also narrowing down helps to understand what it actually protects.
>
> I thought that you would call out unnecessarily delaying other softirq
> handlers. ;-)
>
> But if such delays are a problem (and they might well be), then to
> avoid them on non-rcu_nocb CPUs would instead/also require changing the
> early-exit checks to check for other pending softirqs to the existing
> checks involving time, need_resched, and idle. At which point, entering and
> exiting BH-disabled again doesn't help, other than your point about the
> difference in BH-disabled scopes on rcu_nocb and non-rcu_nocb CPUs.
Wise observation!
>
> Would it make sense to exit rcu_do_batch() if more than some amount
> of time had elapsed and there was some non-RCU softirq pending?
>
> My guess is that the current tlimit checks in rcu_do_batch() make this
> unnecessary.
Right and nobody has complained about it so far.
But I should add a comment explaining the reason for the BH-disabled
section in my series.
Thanks.
>
> Thoughts?
>
> Thanx, Paul
next prev parent reply other threads:[~2020-12-08 22:07 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-08 14:58 One potential issue with concurrent execution of RCU callbacks Paul E. McKenney
2020-12-08 15:54 ` Frederic Weisbecker
2020-12-08 17:19 ` Paul E. McKenney
2020-12-08 17:52 ` Frederic Weisbecker
2020-12-08 18:24 ` Paul E. McKenney
2020-12-08 22:04 ` Frederic Weisbecker [this message]
2020-12-09 0:03 ` Paul E. McKenney
2020-12-09 2:14 ` Boqun Feng
2020-12-10 0:50 ` Paul E. McKenney
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