linux-kernel - Re: [PATCH] rt/threadirqs: put the irq thread handler in a callback

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Message-ID: <alpine.DEB.1.10.0902130046250.15469@gandalf.stny.rr.com>
Date:	Fri, 13 Feb 2009 00:46:44 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rt/threadirqs: put the irq thread handler in a
 callback


On Fri, 13 Feb 2009, Frederic Weisbecker wrote:

> Currently, when a hardirq is threaded, it is processed by do_hardirq()
> which guess the best low-level handler for this irq.
> 
> This makes several branch conditions to check for each irq triggered,
> adding some (very small) latencies since we are in a fastpath (irq disabled)
> of the irq processing.
> 
> So it's better to put these checks only once when the handler of the irq is set
> and then only dereference one pointer to find the appropriate callback.
> 
> This patch makes the irq thread handler a field in struct irq_desc.
> 
> [Note, I'm not sure the check if (!desc->handle_irq_thread) is really
> useful. I've put it to ensure that even an irq_desc which never gone to
> __set_irq_handler() can be handled. But I'm not sure it is possible.]
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Thanks, I'll apply it to my local tree and test it out.

-- Steve

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