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

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Message-ID: <46D3C60B.3050605@vmware.com>
Date:	Mon, 27 Aug 2007 23:51:55 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...ranet.com>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] Add I/O hypercalls for i386 paravirt

Benjamin Herrenschmidt wrote:
> On Wed, 2007-08-22 at 16:25 +1000, Rusty Russell wrote:
>   
>> On Wed, 2007-08-22 at 08:34 +0300, Avi Kivity 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.
>>>>         
>>> Won't these workloads be better off using paravirtualized drivers? 
>>> i.e., do the native drivers with paravirt I/O instructions get anywhere
>>> near the performance of paravirt drivers?
>>>       
>> This patch also means I can kill off the emulation code in
>> drivers/lguest/core.c, which is a real relief.
>>     
>
> Hrm... how do you deal with X doing IOs ?
>
> Ben.
>   

We have an X driver that does minimal performance costing operations.  
As we should and will have for our other drivers.

Zach

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