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

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Message-ID: <20090525050630.GB23032@elte.hu>
Date:	Mon, 25 May 2009 07:06:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
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)


* Avi Kivity <avi@...hat.com> wrote:

> 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.

Yeah. Eventually anything that matters to performance will be 
accelerated by hardware (and properly virtualized), which in turn 
will be faster than any hypercall based approach, right?

	Ingo
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