netdev - Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus

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Message-ID: <4A8A5A7F.5050809@redhat.com>
Date:	Tue, 18 Aug 2009 10:38:39 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	Gregory Haskins <gregory.haskins@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	alacrityvm-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver
 objects

On 08/18/2009 04:08 AM, Anthony Liguori wrote:
> I believe strongly that we should avoid putting things in the kernel 
> unless they absolutely have to be.  I'm definitely interested in 
> playing with vhost to see if there are ways to put even less in the 
> kernel.  In particular, I think it would be a big win to avoid 
> knowledge of slots in the kernel by doing ring translation in 
> userspace.  This implies a userspace transition in the fast path.  
> This may or may not be acceptable.  I think this is going to be a very 
> interesting experiment and will ultimately determine whether my 
> intuition about the cost of dropping to userspace is right or wrong.

I believe with a perfectly scaling qemu this should be feasible.  
Currently qemu is far from scaling perfectly, but inefficient userspace 
is not a reason to put things into the kernel.

Having a translated ring is also a nice solution for migration - 
userspace can mark the pages dirty while translating the receive ring.

Still, in-kernel translation is simple enough that I think we should 
keep it.

-- 
error compiling committee.c: too many arguments to function

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