On Thu, Feb 21, 2013 at 11:02:31AM -0600, Anthony Liguori wrote: > "Michael S. Tsirkin" <m...@redhat.com> writes: > > > 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. > > I mean that: > > 1) the same code path is used regardless of network backend > > 2) QEMU has the ability to manipulate the traffic if it needs/wants to > > 3) the state of the device model is userspace at all times > > 4) QEMU is always the front-line interface communicating with the guest > > Yes, this could be a model where -netdev vhost-net was the backend used > by QEMU. > > > 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. > > Not sure what you mean here. If you are talking about read/write on a > tap file descriptor, I'm not even suggesting that. > > I'm perfectly fine with vhost-net being a -netdev backend. But that's a > very different model than how we use it today. > > Regards, > > Anthony Liguori
It's not hard to make the first step there. Basically just make -netdev vhost-net an alias for -netdev tap, just making vhost=on the default. For non virtio frontends, it needs a driver for vhost-net in userspace, I started a work on this at some point as it would let me write unit tests for virtio, but never finished. Any takers? > > > > > >> > > >> >> 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 > >> >>
