linux-kernel - Re: [PATCH 15/16] rcu: Check for a nocb cpu before trying to spawn nocb threads

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Message-ID: <CAJhHMCDGGTtcW2ENQowKFoujLmqum8yn5ppH1RP=kv5UU+qdPw@mail.gmail.com>
Date:	Wed, 23 Jul 2014 09:14:51 -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 15/16] rcu: Check for a nocb cpu before trying to spawn
 nocb threads

On Wed, Jul 23, 2014 at 8:28 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Jul 23, 2014 at 01:09:52AM -0400, Pranith Kumar wrote:
>> This commit tries to spawn nocb kthreads only when the CPU is marked as a nocb
>> cpu. This is a minor optimization.
>>
>> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>
> This only happens once at boot time, so I am happier with the single check
> at the bottom.  So sorry, but no.
>


Actually this happens whenever a CPU is coming online, but yes, it is
a minor optimization for hotplug.

>                                                         Thanx, Paul
>
>> ---
>>  kernel/rcu/tree_plugin.h | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>> index 541c776..8abff0a 100644
>> --- a/kernel/rcu/tree_plugin.h
>> +++ b/kernel/rcu/tree_plugin.h
>> @@ -1490,7 +1490,8 @@ static void rcu_prepare_kthreads(int cpu)
>>               return;
>>
>>       rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
>> -     rcu_spawn_all_nocb_kthreads(cpu);
>> +     if (rcu_is_nocb_cpu(cpu))
>> +             rcu_spawn_all_nocb_kthreads(cpu);
>>  }
>>
>>  #else /* #ifdef CONFIG_RCU_BOOST */
>> --
>> 2.0.0.rc2
>>
>



-- 
Pranith
--
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