linux-kernel - Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

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Message-ID: <20081109064147.GD7123@il.ibm.com>
Date:	Sun, 9 Nov 2008 08:41:48 +0200
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Greg KH <greg@...ah.com>, Matthew Wilcox <matthew@....cx>,
	H L <swdevyid@...oo.com>, Yu Zhao <yu.zhao@...el.com>,
	randy.dunlap@...cle.com, grundler@...isc-linux.org, achiang@...com,
	linux-pci@...r.kernel.org, rdreier@...co.com,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	mingo@...e.hu, Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

On Thu, Nov 06, 2008 at 04:40:21PM -0600, Anthony Liguori wrote:

> We've been talking about avoiding hardware passthrough entirely and
> just backing a virtio-net backend driver by a dedicated VF in the
> host.  That avoids a huge amount of guest-facing complexity, let's
> migration Just Work, and should give the same level of performance.

I don't believe that it will, and every benchmark I've seen or have
done so far shows a significant performance gap between virtio and
direct assignment, even on 1G ethernet. I am willing however to
reserve judgement until someone implements your suggestion and
actually measures it, preferably on 10G ethernet.

No doubt device assignment---and SR-IOV in particular---are complex,
but I hardly think ignoring it as you seem to propose is the right
approach.

Cheers,
Muli
-- 
The First Workshop on I/O Virtualization (WIOV '08)
Dec 2008, San Diego, CA, http://www.usenix.org/wiov08/
                       <->
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