linux-kernel - Re: [PATCH 0/6] rcu: Remove several redundant memory barriers

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Message-ID: <xhsmhjzjvgevl.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Wed, 15 May 2024 19:32:30 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>, LKML
 <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>, "Paul E . McKenney"
 <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Joel Fernandes
 <joel@...lfernandes.org>, Neeraj Upadhyay <neeraj.upadhyay@....com>,
 Uladzislau Rezki <urezki@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 rcu <rcu@...r.kernel.org>
Subject: Re: [PATCH 0/6] rcu: Remove several redundant memory barriers

On 15/05/24 14:53, Frederic Weisbecker wrote:
> Reviewing Valentin's patchset made me stare at some memory barriers
> on the way.

Sorry not sorry? :-)

> Here is some removal proposal. Some may be beneficial on
> runtime (fqs snapshot with potentially as many smp_mb() as the number
> of online CPUs for each GP). Some happen on more rare path. In any
> case they clarify code reviews so we don't stumble upon mysterious
> barriers.
>
> Thanks.
>
> Frederic Weisbecker (6):
>   rcu: Remove full ordering on second EQS snapshot
>   rcu: Remove superfluous full memory barrier upon first EQS snapshot
>   rcu/exp: Remove superfluous full memory barrier upon first EQS
>     snapshot
>   rcu: Remove full memory barrier on boot time eqs sanity check
>   rcu: Remove full memory barrier on RCU stall printout
>   rcu/exp: Remove redundant full memory barrier at the end of GP
>
>  .../Tree-RCU-Memory-Ordering.rst              |  6 +++---
>  kernel/rcu/tree.c                             | 21 +++++++------------
>  kernel/rcu/tree_exp.h                         | 16 +++++++++++---
>  kernel/rcu/tree_stall.h                       |  4 ++--
>  4 files changed, 26 insertions(+), 21 deletions(-)
>
> --
> 2.44.0