Re: [Qemu-devel] [PATCH 0/9] introduce virtio net dataplane

[Anthony Liguori]

"Michael S. Tsirkin" <address@hidden> writes:

> On Thu, Feb 21, 2013 at 08:54:44PM +0800, Liu Ping Fan wrote:
>> This is a emulation to virtio-blk dataplane, which push the data
>> handling out of biglock. And it is a try to implement this process
>> in userspace, while vhost-net in kernel.
>
> What's the motivation for doing this?

I haven't looked carefully at the patches, but I don't think we should
"cheat" when it comes to virtio-net.  I think it's useful to have a
baseline proof of concept but I think we should focus on making the
network layer re-entrant.

In terms of why even bother, if we can make virtio-net a viable
alternative to vhost-net, it's a huge win.  Being in userspace is a huge
advantage.

I understand the challenges with zero-copy but we really need a proper
userspace implementation to determine how much it really matters.
Zero-copy tap is also not entirely outside the realm of possibility.

>> The iperf's result show it improving the perfermance of base line,
>> but still slower than vhost-net (maybe the rx path need optimized).
>> 
>> Todo:
>> implement fine lock for net-subsystem
>
> vhost-net is currently the only way to get zero copy transmit
> on linux (and zero copy receive in the future)
> so at least in theory it'll always be faster.

It might always be faster.  But that doesn't mean we should limit the
performance of virtio-net in userspace.  Some people may be willing to
take a small performance hit in order to obtain the security offered by
being in userspace.

Regards,

Anthony Liguori

>
>> Liu Ping Fan (9):
>>   vring: split the modification and publish of used ring
>>   vring: introduce vring_restore() to restore from img
>>   event poll: make epoll work for normal fd
>>   event poll: pass event type to event callback
>>   event poll: enable event poll handle more than one event each time
>>   virtio net: introduce dataplane for virtio net
>>   tap: make tap peer work on dedicated data-plane thread
>>   virtio net: enable dataplane for virtio net
>>   configure: make virtio net dataplane configurable
>> 
>>  configure                  |   12 ++
>>  hw/dataplane/Makefile.objs |    4 +-
>>  hw/dataplane/event-poll.c  |   69 +++++--
>>  hw/dataplane/event-poll.h  |   14 ++-
>>  hw/dataplane/virtio-blk.c  |    8 +-
>>  hw/dataplane/virtio-net.c  |  444 
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  hw/dataplane/virtio-net.h  |   32 ++++
>>  hw/dataplane/vring.c       |   37 ++++
>>  hw/dataplane/vring.h       |    3 +
>>  hw/virtio-net.c            |   94 +++++-----
>>  hw/virtio-net.h            |   64 +++++++
>>  hw/virtio-pci.c            |    2 +-
>>  include/net/tap.h          |    6 +
>>  net/tap.c                  |   92 +++++++++-
>>  14 files changed, 806 insertions(+), 75 deletions(-)
>>  create mode 100644 hw/dataplane/virtio-net.c
>>  create mode 100644 hw/dataplane/virtio-net.h
>> 
>> -- 
>> 1.7.4.4
>>