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

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Message-ID: <87d4h7pnnm.fsf@basil.nowhere.org>
Date:	Fri, 07 Nov 2008 16:21:33 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Matthew Wilcox <matthew@....cx>,
	"Fischer, Anna" <anna.fischer@...com>, Greg KH <greg@...ah.com>,
	H L <swdevyid@...oo.com>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"Chiang, Alexander" <achiang@...com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>
Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

Anthony Liguori <anthony@...emonkey.ws> writes:
>
> What we would rather do in KVM, is have the VFs appear in the host as
> standard network devices.  We would then like to back our existing PV
> driver to this VF directly bypassing the host networking stack.  A key
> feature here is being able to fill the VF's receive queue with guest
> memory instead of host kernel memory so that you can get zero-copy
> receive traffic.  This will perform just as well as doing passthrough
> (at least) and avoid all that ugliness of dealing with SR-IOV in the
> guest.

But you shift a lot of ugliness into the host network stack again.
Not sure that is a good trade off.

Also it would always require context switches and I believe one
of the reasons for the PV/VF model is very low latency IO and having
heavyweight switches to the host and back would be against that.

-Andi

-- 
ak@...ux.intel.com
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