linux-kernel - Re: [PATCH 0/8] tip related: radix tree for spareseirq and logical flat clean up

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Date:	Fri, 12 Feb 2010 19:49:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH  0/8] tip related: radix tree for spareseirq and logical
 flat clean up

On 02/12/2010 07:44 PM, Eric W. Biederman wrote:
> 
> Thanks for keeping this work alive.
> 

Indeed.  I am hoping to put this in tip tomorrow or so.

> I just skimmed through do_IRQ and I happened to notice that
> we have an unnecessary inefficiency that using a radix tree for
> irq_to_desc will magnify.
> 
> handle_irq should take an struct irq_desc * instead of a unsigned int irq.
> 
> and the per cpu vector_irq array should become a per cpu vector_desc array.
> 
> As soon as irq_to_desc is more than &irq_desc[irq] this saves us work
> and cache line misses  at the cost of a simple code cleanup.

Good catch.  I haven't looked through the details yet, but I presume
this can be done on top of this changeset?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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