linux-kernel - Re: [RFC PATCH v2 15/19] kvm: add dynamic IRQ support

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Date:	Mon, 13 Apr 2009 13:44:30 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Avi Kivity <avi@...hat.com>
CC:	linux-kernel@...r.kernel.org, agraf@...e.de, pmullaney@...ell.com,
	pmorreale@...ell.com, anthony@...emonkey.ws, rusty@...tcorp.com.au,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	bhutchings@...arflare.com, andi@...stfloor.org, gregkh@...e.de,
	herber@...dor.apana.org.au, chrisw@...s-sol.org,
	shemminger@...tta.com
Subject: Re: [RFC PATCH v2 15/19] kvm: add dynamic IRQ support

Avi Kivity wrote:
>>  
>
> Given that you're using the apic to inject the IRQ, you'll need an
> EOI.  So what's the difference between dynirq and MSI, performance wise?
>

I would have loved to eliminate that EOI completely, but that is a much
broader problem to solve ;)

Actually dynirq wasnt introduced as a performance alternative over MSI. 
Rather, I was trying to eliminate the complexity of needing to sync
between the userspace PCI emulation and the in kernel models.

However, its moot.  Since v2 introduce virtio-vbus, I now have a much
clearer picture of what is needed here, and v3 will simply integrate
with MSI interrupts and drop dynirq completely.  So please ignore this
patch.

-Greg


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