Stefan Hajnoczi <stefanha at gmail.com> writes:> On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty at rustcorp.com.au> wrote: >> Anthony Liguori <anthony at codemonkey.ws> writes: >>> Rusty Russell <rusty at rustcorp.com.au> writes: >>>> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote: >>>>> FWIW, I think what's more interesting is using vhost-net as a networking >>>>> backend with virtio-net in QEMU being what's guest facing. >>>>> >>>>> In theory, this gives you the best of both worlds: QEMU acts as a first >>>>> line of defense against a malicious guest while still getting the >>>>> performance advantages of vhost-net (zero-copy). >>>>> >>>> It would be an interesting idea if we didn't already have the vhost >>>> model where we don't need the userspace bounce. >>> >>> The model is very interesting for QEMU because then we can use vhost as >>> a backend for other types of network adapters (like vmxnet3 or even >>> e1000). >>> >>> It also helps for things like fault tolerance where we need to be able >>> to control packet flow within QEMU. >> >> (CC's reduced, context added, Dmitry Fleytman added for vmxnet3 thoughts). >> >> Then I'm really confused as to what this would look like. A zero copy >> sendmsg? We should be able to implement that today. >> >> On the receive side, what can we do better than readv? If we need to >> return to userspace to tell the guest that we've got a new packet, we >> don't win on latency. We might reduce syscall overhead with a >> multi-dimensional readv to read multiple packets at once? > > Sounds like recvmmsg(2).Could we map this to mergable rx buffers though? Regards, Anthony Liguori> > Stefan
On Thu, May 30, 2013 at 08:40:47AM -0500, Anthony Liguori wrote:> Stefan Hajnoczi <stefanha at gmail.com> writes: > > > On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty at rustcorp.com.au> wrote: > >> Anthony Liguori <anthony at codemonkey.ws> writes: > >>> Rusty Russell <rusty at rustcorp.com.au> writes: > >>>> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote: > >>>>> FWIW, I think what's more interesting is using vhost-net as a networking > >>>>> backend with virtio-net in QEMU being what's guest facing. > >>>>> > >>>>> In theory, this gives you the best of both worlds: QEMU acts as a first > >>>>> line of defense against a malicious guest while still getting the > >>>>> performance advantages of vhost-net (zero-copy). > >>>>> > >>>> It would be an interesting idea if we didn't already have the vhost > >>>> model where we don't need the userspace bounce. > >>> > >>> The model is very interesting for QEMU because then we can use vhost as > >>> a backend for other types of network adapters (like vmxnet3 or even > >>> e1000). > >>> > >>> It also helps for things like fault tolerance where we need to be able > >>> to control packet flow within QEMU. > >> > >> (CC's reduced, context added, Dmitry Fleytman added for vmxnet3 thoughts). > >> > >> Then I'm really confused as to what this would look like. A zero copy > >> sendmsg? We should be able to implement that today. > >> > >> On the receive side, what can we do better than readv? If we need to > >> return to userspace to tell the guest that we've got a new packet, we > >> don't win on latency. We might reduce syscall overhead with a > >> multi-dimensional readv to read multiple packets at once? > > > > Sounds like recvmmsg(2). > > Could we map this to mergable rx buffers though? > > Regards, > > Anthony LiguoriYes because we don't have to complete buffers in order.> > > > Stefan
"Michael S. Tsirkin" <mst at redhat.com> writes:> On Thu, May 30, 2013 at 08:40:47AM -0500, Anthony Liguori wrote: >> Stefan Hajnoczi <stefanha at gmail.com> writes: >> >> > On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty at rustcorp.com.au> wrote: >> >> Anthony Liguori <anthony at codemonkey.ws> writes: >> >>> Rusty Russell <rusty at rustcorp.com.au> writes: >> >>>> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote: >> >>>>> FWIW, I think what's more interesting is using vhost-net as a networking >> >>>>> backend with virtio-net in QEMU being what's guest facing. >> >>>>> >> >>>>> In theory, this gives you the best of both worlds: QEMU acts as a first >> >>>>> line of defense against a malicious guest while still getting the >> >>>>> performance advantages of vhost-net (zero-copy). >> >>>>> >> >>>> It would be an interesting idea if we didn't already have the vhost >> >>>> model where we don't need the userspace bounce. >> >>> >> >>> The model is very interesting for QEMU because then we can use vhost as >> >>> a backend for other types of network adapters (like vmxnet3 or even >> >>> e1000). >> >>> >> >>> It also helps for things like fault tolerance where we need to be able >> >>> to control packet flow within QEMU. >> >> >> >> (CC's reduced, context added, Dmitry Fleytman added for vmxnet3 thoughts). >> >> >> >> Then I'm really confused as to what this would look like. A zero copy >> >> sendmsg? We should be able to implement that today. >> >> >> >> On the receive side, what can we do better than readv? If we need to >> >> return to userspace to tell the guest that we've got a new packet, we >> >> don't win on latency. We might reduce syscall overhead with a >> >> multi-dimensional readv to read multiple packets at once? >> > >> > Sounds like recvmmsg(2). >> >> Could we map this to mergable rx buffers though? >> >> Regards, >> >> Anthony Liguori > > Yes because we don't have to complete buffers in order.What I meant though was for GRO, we don't know how large the received packet is going to be. Mergable rx buffers lets us allocate a pool of data for all incoming packets instead of allocating max packet size * max packets. recvmmsg expects an array of msghdrs and I presume each needs to be given a fixed size. So this seems incompatible with mergable rx buffers. Regards, Anthony Liguori> >> > >> > Stefan