linux-kernel - Re: Long playing threaded interrupt handlers

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Message-ID: <20100602074520.GI3713@core.coreip.homeip.net>
Date:	Wed, 2 Jun 2010 00:45:20 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Long playing threaded interrupt handlers

On Wed, Jun 02, 2010 at 09:19:21AM +0200, Thomas Gleixner wrote:
> On Wed, 2 Jun 2010, Dmitry Torokhov wrote:
> 
> > HI Thomas,
> > 
> > The threaded IRQ infrastructure that went into the kernel is extremely
> > helpful, however in the input land there are quite a few devices that
> > require polling after an IRQ has been raised.
> > 
> > Currently most such drivers, instead of threaded interrupts, still use
> > [delayed] work to do the polling, and still face the issue of shutting
> > down interrupt and scheduled work in a raceless way leaving irq enable
> > counter balanced. Is it allowed to have threaded ISR execute for
> > extended a amount of time, and do the required polling, provided that
> > ISR does certain checks to finish promply in case when we unbind the
> > driver or try to suspend the device?
> 
> Sure, why not ?

Great, that is what I wanted to hear!

> The only thing we need to think about is when the poll
> is busy polling for a long time, then we need to lower the irq thread
> priority to SCHED_OTHER in order not to hog the CPU.

I don't think the drivers will actively polling for a long time, they
are likely to poll and then sleep for some time (100-200-300 msecs), so
typical loop will be:

handler()
{
	while (!shutdown_or_suspend) {
		poll_device();

		if (all_up)
			break;

		msleep(poll_interval);
	}

	return IRQ_HANDLED;
}

Thanks.

-- 
Dmitry
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