linux-kernel - Re: [PATCH] RFC: Set irq thread to RT priority on creation

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Date:	Thu, 30 May 2013 21:50:41 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Ivo Sieben <meltedpianoman@...il.com>,
	RT <linux-rt-users@...r.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RFC: Set irq thread to RT priority on creation

On Thu, 30 May 2013, Steven Rostedt wrote:

> On Thu, 2013-05-30 at 16:07 +0200, Thomas Gleixner wrote:
> 
> > > This patch solves an issue for me where a device driver is expected to handle an
> > > interrupt immediatly after irq handlers are installed and interrupts enabled.
> > 
> > You miss to explain what kind of issue that is.
> 
> I could envision the case where the interrupt is initialized but doesn't
> go off until much later. If it never ran, then it would still be in
> SCHED_OTHER(), and that first interrupt could have a large delay.

Nope. As Ivo explained it's about an interrupt coming in right away,
i.e. before __setup_irq() reaches:

        if (new->thread)
	   wake_up_process(new->thread);

The ones which come much later do not have that issue as the thread
code already sits in the waiting loop and already adjusted the
priority.

Thanks,

	tglx

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