linux-kernel - Re: [PATCH] x86: fix probe_nr

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Message-ID: <48ADFFD2.7030309@goop.org>
Date:	Thu, 21 Aug 2008 16:52:50 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alex Nixon <alex.nixon@...rix.com>
Subject: Re: [PATCH] x86: fix probe_nr_irqs for xen

Yinghai Lu wrote:
> On Thu, Aug 21, 2008 at 4:33 PM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>   
>> Yinghai Lu wrote:
>>     
>>> otherwise Xen is _completely_ unusable with 5 or more VCPUs.
>>> ( when !CONFIG_HAVE_SPARSE_IRQ)
>>>
>>> based on Alex's patch
>>>
>>> also add +1 offset after redir_entries
>>>
>>> Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
>>> Cc: Alex Nixon <alex.nixon@...rix.com>
>>>
>>>       
>> Looks good to me.  We can fix this in a better way later.
>>     
>
> later could set CONFIG_HAVE_SPARSE_IRQ to true by default.
>   

Well, perhaps.  But we can use vectors rather than IRQs for Xen event
channel mappings, which will save us from having to allocate lots of
per-cpu irqs.

Also, implementing probe_nr_irqs() in a more generic (rather than
io_apic-specific) way.  Using some interface that queries each irq chip
for how many irqs it supports, or something.

    J
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