linux-kernel - Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR

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Date:	Wed, 20 Aug 2008 16:23:06 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Alex Nixon (Intern)" <Alex.Nixon@...rix.com>
CC:	Yinghai Lu <yhlu.kernel@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] X86: Change the default value of nr_irqs from 32 to NR_IRQs

Alex Nixon (Intern) wrote:
> I'm not sure about the general case, but Xen does not (Jeremy correct
> me if I'm wrong).
>

No, no apics of any kind in the PV domU case.

> Unless I'm missing something (which I may well be; I'm new to this
> area of code), it seems more logical anyway to default back to the
> calculated system-specific value (NR_IRQS), instead of 32, which seems
> rather arbitrary.
>

I think the patch looks fine for now.  But now that we seem to have
unified the use of vectors (I haven't looked at the current code closely
yet), I'd like to move Xen to mapping event channels -> vectors rather
than IRQs, and have the per-cpu event channels share an irq.  That will
dramatically decrease the irq requirements for a PV domU (to 6 irqs +
devices, rather than 6/cpu + devices; a typical domain may only need 10
irqs overall).

    J

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