linux-kernel - Re: question about disabling interrupts for workqueue pool?

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Message-ID: <20130625230129.GA30407@mtj.dyndns.org>
Date:	Tue, 25 Jun 2013 16:01:29 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clark@...hat.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: question about disabling interrupts for workqueue pool?

Hello, Steven.

On Tue, Jun 25, 2013 at 06:52:34PM -0400, Steven Rostedt wrote:
> Now my question is, are those local_irq_*() calls just for synchronizing
> with sched RCU? If so, can you use rcu_read_lock_sched() instead?

Hmmm... using local_irq_disable/enable() is more consistent as
irq-safe locks are used widely in workqueue.  Also, using
rcu_read_lock_sched() would mean that we'll have
spin_lock_irq_save/restore() nested inside preempt_disable/enable(),
which is a bit silly in upstream kernel.

That said, both paths you pointed out are rather cold, so I don't
think it'd matter.  Please feel free to send a patch with comment
explaining why local irq flipping, which fits better there, isn't
being used.

Thanks.

-- 
tejun
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