linux-kernel - Re: [GIT PULL] Xen APIC hooks (with io_apic

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Message-ID: <20090519123548.GA26439@elte.hu>
Date:	Tue, 19 May 2009 14:35:48 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [GIT PULL] Xen APIC hooks (with io_apic_ops)


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Hi Ingo,
> 
> Here's a revised set of the Xen APIC changes which adds 
> io_apic_ops to allow Xen to intercept IO APIC access operations.

In a previous discussion you said:

> IO APIC operations are not even slightly performance critical? Are 
> they ever used on the interrupt delivery path?

Since they are not performance critical, then why doesnt Xen catch 
the IO-APIC accesses, and virtualizes the device?

If you want to hook into the IO-APIC code at such a low level, why 
dont you hook into the _hardware_ API - i.e. catch those 
setup/routing modifications to the IO-APIC space. No Linux changes 
are needed in that case.

	Ingo
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