Re: [PATCHv5 3/3] vhost_net: a kernel-level virtio server

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On 09/15/2009 04:50 PM, Gregory Haskins wrote:
Why?  vhost will call get_user_pages() or copy_*_user() which ought to
do the right thing.
I was speaking generally, not specifically to Ira's architecture.  What
I mean is that vbus was designed to work without assuming that the
memory is pageable.  There are environments in which the host is not
capable of mapping hvas/*page, but the memctx->copy_to/copy_from
paradigm could still work (think rdma, for instance).

Sure, vbus is more flexible here.

As an aside: a bigger issue is that, iiuc, Ira wants more than a single
ethernet channel in his design (multiple ethernets, consoles, etc).  A
vhost solution in this environment is incomplete.

Why?  Instantiate as many vhost-nets as needed.
a) what about non-ethernets?

There's virtio-console, virtio-blk etc. None of these have kernel-mode servers, but these could be implemented if/when needed.

b) what do you suppose this protocol to aggregate the connections would
look like? (hint: this is what a vbus-connector does).

You mean multilink?  You expose the device as a multiqueue.

c) how do you manage the configuration, especially on a per-board basis?

pci (for kvm/x86).

Actually I have patches queued to allow vbus to be managed via ioctls as
well, per your feedback (and it solves the permissions/lifetime
critisims in alacrityvm-v0.1).

That will make qemu integration easier.

  The only difference is the implementation.  vhost-net
leaves much more to userspace, that's the main difference.
Also,

*) vhost is virtio-net specific, whereas vbus is a more generic device
model where thing like virtio-net or venet ride on top.

I think vhost-net is separated into vhost and vhost-net.

*) vhost is only designed to work with environments that look very
similar to a KVM guest (slot/hva translatable).  vbus can bridge various
environments by abstracting the key components (such as memory access).

Yes.  virtio is really virtualization oriented.

*) vhost requires an active userspace management daemon, whereas vbus
can be driven by transient components, like scripts (ala udev)

vhost by design leaves configuration and handshaking to userspace. I see it as an advantage.

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

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