linux-kernel - Re: preempt_check

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Message-ID: <20140307121423.GI3852@intel.com>
Date:	Fri, 7 Mar 2014 14:14:23 +0200
From:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	mingo@...nel.org
Subject: Re: preempt_check_resched() gone?

On Thu, Mar 06, 2014 at 09:52:42PM +0100, Thomas Gleixner wrote:
> On Thu, 6 Mar 2014, Ville Syrjälä wrote:
> > Hi,
> > 
> > It appears preempt_check_resched() is no longer available for modules
> > since [1]. So now I'm left wondering what is one supposed to use after
> > local_irq_enable(). Documentation/preempt-locking.txt still says one
> > should do a check, but the tool to do that was taken away.
> 
> The documentation is slightly misleading. The point is:
> 
> If you have an irq disabled section and you do a wakeup inside this
> section which causes the need resched bit to be set, then
> local_irq_enable/restore wont do an preemption check.
> 
> If you merily poke at a few device registers then nothing will set
> need resched and you're good.

OK. There are a few extra things that get called while irqs are
disabled: prepare_to_wait(), finish_wait(), mod_timer(),
spin_{lock,unlock}(). Based on a quick glance none of those should
do anything I need to worry about, so I'll just drop
preempt_check_resched() from my code.

Thanks.

-- 
Ville Syrjälä
Intel OTC
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