linux-kernel - Re: [PATCH rcu 3/6 v2] rcu/exp: Remove superfluous full memory barrier upon first EQS snapshot

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Date: Fri, 28 Jun 2024 13:20:55 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org
Subject: Re: [PATCH rcu 3/6 v2] rcu/exp: Remove superfluous full memory
 barrier upon first EQS snapshot

Le Thu, Jun 27, 2024 at 11:53:29AM -0700, Paul E. McKenney a écrit :
> On Thu, Jun 27, 2024 at 01:36:58PM +0200, Frederic Weisbecker wrote:
> > When the grace period kthread checks the extended quiescent state
> > counter of a CPU, full ordering is necessary to ensure that either:
> 
> Just to make sure that I understand...
> 
> I need to replace these commits in -rcu:
> 
> da979d0162fc6 rcu: Remove full ordering on second EQS snapshot
> 6411f4185f657 rcu: Remove superfluous full memory barrier upon first EQS snapshot
> dec56ca5f1c34 rcu/exp: Remove superfluous full memory barrier upon first EQS snapshot
> 
> With these three patches, and keep these three commits as they are?
> 
> d43a302fc08a5 rcu: Remove full memory barrier on boot time eqs sanity check
> b1c36aa90cbf1 rcu: Remove full memory barrier on RCU stall printout
> 64d68f1d53f77 rcu/exp: Remove redundant full memory barrier at the end of GP

Exactly! Those were the precisions I forgot to mention.

Thanks.