On Tuesday 17 June 2008 00:02:55 Anthony Liguori wrote: > There's nothing that prevents zero-copy to be implemented for tun > without vringfd. In fact, I seem to recall that your earlier patches > implemented zero-copy :-)
They didn't actually work. You need to block until the data isn't being used any more (thread pool anyone?), or implement an aio interface. > I like the vringfd model and I think it's a good way to move forward. > My concern is that it introduces an extra syscall in the TX path. Right > now, we do a single write call whereas with vringfd we need to insert > the TX packet into the queue, do a notify, and then wait for indication > that the TX has succeeded. If the guest wants notification of xmit, yes you need another syscall for that. But it often doesn't (note: current vring tun ignored the NO_NOTIFY flag, but one thing at a time). > I know we'll win with TSO but we don't need vringfd for TSO. The jury's > still out IMHO as to whether we should do vringfd or just try to merge > TSO tun patches. Note that we can do TSO in userspace, too. No syscall reduction, but an VM exit reduction. Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
