"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: > On Thu, May 30, 2013 at 08:40:47AM -0500, Anthony Liguori wrote: >> Stefan Hajnoczi <stefanha@xxxxxxxxx> writes: >> >> > On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: >> >> Anthony Liguori <anthony@xxxxxxxxxxxxx> writes: >> >>> Rusty Russell <rusty@xxxxxxxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
