Re: [PATCH 0/7] AlacrityVM guest drivers Reply-To:

[Gregory Haskins <gregory.haskins@gmail.com>]

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[not sure if it was intentional, but you dropped the CC list.
Therefore, I didn't see this until I caught up on my kvm@vger reading]

Pantelis Koukousoulas wrote:
> How hard would it be to implement virtio over vbus and perhaps the
> virtio-net backend?

It should be relatively trivial.  I have already written the transport
(called virtio-vbus) that would allow the existing front-end
(virtio-net) to work without modification.

http://lkml.org/lkml/2009/4/21/427

All that is needed is to take venet-tap as an example and port it to
something virtio compatible (via that patch I posted) on the backend.  I
have proposed this as an alternative to venet, but so far I have not had
any takers to help with this effort.  Likewise, I am too busy with the
infrastructure to take this on myself.


> 
> This would leave only one variable in the comparison, clear misconceptions and
> make evaluation easier by judging each of vbus, venet etc separately on its own
> merits.
> 
> The way things are now, it is unclear exactly where those performance
> improvements are coming from (or how much each component contributes)
> because there are too many variables.
> 
> Replacing virtio-net by venet would be a hard proposition if only because
> virtio-net has (closed source) windows drivers available. There has to be
> shown that venet by itself does something significantly better that
> virtio-net can't be modified to do comparably well.

I am not proposing anyone replace virtio-net.  It will continue to work
fine despite the existence of an alternative, and KVM can continue to
standardize on it if that is what KVM wants to do.

> 
> Having venet in addition to virtio-net is also difficult, given that having only
> one set of paravirtual drivers in the kernel was the whole point behind virtio.

As it stands right now, virtio-net fails to meet my performance goals,
and venet meets them (or at least, gets much closer, but I will not
rest..).  So, at least for AlacrityVM, I will continue to use and
promote it when performance matters.  If at some time in the future I
can get virtio-net to work in my environment in a comparable and
satisfactory way, I will consider migrating to it and deprecating venet.

Until then, having two drivers is ok, and no-one has to use the one they
don't like.  I certainly do not think having more than one driver that
speaks 802.x ethernet in the kernel tree is without precedent. ;)

Kind Regards,
-Greg


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