linux-kernel - Re: [PATCH] Add I/O hypercalls for i386 paravirt

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Date:	Wed, 22 Aug 2007 23:15:11 +0100
From:	James Courtier-Dutton <James@...erbug.co.uk>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Zachary Amsden <zach@...are.com>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Avi Kivity <avi@...ranet.com>
Subject: Re: [PATCH] Add I/O hypercalls for i386 paravirt

Jeremy Fitzhardinge wrote:
> Zachary Amsden wrote:
>> This patch provides hypercalls for the i386 port I/O instructions,
>> which vastly helps guests which use native-style drivers.  For certain
>> VMI workloads, this provides a performance boost of up to 30%.  We
>> expect KVM and lguest to be able to achieve similar gains on I/O
>> intensive workloads.
> 
> Two comments:
> 
> - I should dust off my "break up paravirt_ops" patch, and this would fit
> nicely into it (I think we already discussed this)
> 
> - What happens if you *don't* want to pv some of the io instructions? 
> What if you have a device which is directly exposed to the guest?


If one could directly expose a device to the guest, this feature could
be extremely useful for me.
Is it possible? How would it manage to handle the DMA bus mastering?

James
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