Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <5bd5ee4a-710a-96bc-abe8-772b2e60f478@efficios.com>
Date:   Tue, 20 Dec 2022 14:01:30 -0500
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.0
Subject: Re: [RFC 0/2] srcu: Remove pre-flip memory barrier
Content-Language: en-US
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>
References: <6438d903-ab97-48c7-c338-9f0bc2686f94@efficios.com>
 <7A9876BA-C375-42A7-A5C9-FD940D2898D7@joelfernandes.org>
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <7A9876BA-C375-42A7-A5C9-FD940D2898D7@joelfernandes.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 2022-12-20 13:29, Joel Fernandes wrote:
> 

> I do want to finish my memory barrier studies of SRCU over the holidays since I have been deep in the hole with that already. Back to the post flip memory barrier here since I think now even that might not be needed…

I strongly suspect the memory barrier after flip is useless for the same 
reasons I mentioned explaining why the barrier before the flip is useless.

However, we need to double-check that we have memory barriers at the 
beginning and end of synchronize_srcu, and between load of "unlock" 
counters and load of "lock" counters.

Where is the barrier at the beginning of synchronize_srcu ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com