linux-kernel - Re: [PATCH 04/16] rcu: Remove redundant check for an online CPU

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Message-ID: <CAJhHMCAQ7+HzXfH7E3LNbUVG_zf-1edj6yPBHQ9wtbTrBAoa7A@mail.gmail.com>
Date:	Wed, 23 Jul 2014 09:23:47 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"open list:READ-COPY UPDATE..." <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/16] rcu: Remove redundant check for an online CPU

On Wed, Jul 23, 2014 at 8:09 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Jul 23, 2014 at 01:09:41AM -0400, Pranith Kumar wrote:
>> rcu_prcess_callbacks() is the softirq handler for RCU which is raised from
>> invoke_rcu_core() which is called from __call_rcu_core().
>>
>> Each of these three functions checks if the cpu is online. We can remove the
>> redundant ones. This commit removes one of these redundant check.
>>
>> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>
> Sorry, but no.  There can be a long delay between raise_softirq() and
> this function starting, particularly if ksoftirqd gets involved.  The
> CPU could easily go offline in the meantime.
>

That makes sense. I guess one of the other two checks in
__call_rcu_core() or invoke_rcu_core() can go then?

-- 
Pranith
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