On Mon, 2007-04-09 at 10:10 +0300, Avi Kivity wrote: > Rusty Russell wrote: > > I'm a little puzzled by your response. Hmm... > > > > lguest's userspace network frontend does exactly as many copies as > > Ingo's in-host-kernel code. One from the Guest, one to the Guest. > > kvm pvnet is suboptimal now. The number of copies could be reduced by > two (to zero), by constructing an skb that points to guest memory. > Right now, this can only be done in-kernel.
Sorry, you lost me here. You mean both input and output copies can be eliminated? Or are you talking about another two copies somewhere? But I don't get this "we can enhance the kernel but not userspace" vibe 8( > With current userspace networking interfaces, one cannot build a network > device that has less than one copy on transmit, because sendmsg() *must* > copy the data (as there is no completion notification). Why are you talking about sendmsg()? Perhaps this is where we're getting tangled up. We're dealing with the tun/tap device here, not a socket. > sendfilev(), > even if it existed, cannot be used: it is copyless, but lacks completion > notification. It is useful only on unchanging data like read-only files. Again, sendfile is a *much* harder problem than sending a single packet once, which is the question here. Rusty. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
