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

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Date:	Sat, 13 Feb 2010 14:12:57 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	ebiederm@...ssion.com, "H. Peter Anvin" <hpa@...or.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
Subject: Re: [PATCH  0/8] tip related: radix tree for spareseirq and logical flat clean up

I don't have the code in front of me, but I think that change should be OK.  Xen just wants to initiate interrupt delivery for a given irq.  At least for x86; I won't make any claims for ia64.

     J

ebiederm@...ssion.com wrote:

>"H. Peter Anvin" <hpa@...or.com> writes:
>
>> 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?
>
>Codewise the changes should be completely independent.
>
>
>
>Probably the trickiest bit is that drivers/xen/events.c calls handle_irq
>and makes handle_irq on ia64 a wrapper for __do_IRQ.
>
>Jeremy is there any good reason why drivers/xen/events.c does not just do:
>
>desc = irq_to_desc(irq);
>if (desc)
>	generic_handle_irq_desc(irq, desc);
>
>And instead introduces a weird one-off xen specific multi-arch function?
>
>
>Eric
>

-- 
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