On Thu, Feb 21, 2013 at 10:15:58AM -0600, Anthony Liguori wrote: > "Michael S. Tsirkin" <m...@redhat.com> 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.
This is exactly what we have, vhost-net is the interface we use for asynchronous communication. If you want to add yet another asynchronous interface in kernel, it's certainly doable but then what's the point? > >> 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 By 'being in userspace' I presume you mean the ring processing code. Ring processing can be done in userspace if you are ready to use the synchronous read/write operations, skipping this bunch of code might improve security. But it requires a data copy almost by definition. > > > >> 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 > >>
