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

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Message-ID: <4A1A24C0.20701@redhat.com>
Date:	Mon, 25 May 2009 07:55:28 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	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)

Ingo Molnar wrote:
>> We do something similar for Windows (by patching it) very 
>> successfully; Windows likes to touch the APIC TPR ~ 100,000 times 
>> per second, usually without triggering an interrupt.  We hijack 
>> these writes, do the checks in guest context, and only exit if the 
>> TPR write would trigger an interrupt.
>>     
>
> I suspect you aware of that this is about the io-apic not the local 
> APIC. The local apic methods are already driver-ized - and they sit 
> closer to the CPU so they matter more to performance.
>   

Yeah, I gave this as an example.  It's very different -- io-apic vs. 
local apic, paravirtualization vs. patching the guest behind its back, 
Linux vs. Windows.

Of course if we hook the io-apic EOI we'll want to hook the local apic 
EOI as well.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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