From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: updated: kvm networking todo wiki Date: Thu, 30 May 2013 09:41:07 -0500 Message-ID: <8761y034zg.fsf@codemonkey.ws> References: <20130523085034.GA16142@redhat.com> <519F35B7.6010408@redhat.com> <20130524113542.GA7046@redhat.com> <8738tctrox.fsf@codemonkey.ws> <20130524140024.GA12024@redhat.com> <87li6yodgq.fsf@rustcorp.com.au> <87k3miq6sw.fsf@codemonkey.ws> <87r4gpkplc.fsf@rustcorp.com.au> <87k3mg60ww.fsf@codemonkey.ws> <20130530134449.GA31649@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm , qemu-devel , Linux Virtualization , herbert@gondor.hengli.com.au, netdev@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20130530134449.GA31649@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org "Michael S. Tsirkin" writes: > On Thu, May 30, 2013 at 08:40:47AM -0500, Anthony Liguori wrote: >> Stefan Hajnoczi writes: >> >> > On Thu, May 30, 2013 at 7:23 AM, Rusty Russell wrote: >> >> Anthony Liguori writes: >> >>> Rusty Russell 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