On Tue, Sep 14, 2010 at 05:21:13PM +0200, Arnd Bergmann wrote: > On Tuesday 14 September 2010, Shirley Ma wrote: > > On Tue, 2010-09-14 at 11:12 +0200, Avi Kivity wrote: > > > > > That's what io_submit() is for. Then io_getevents() tells you what > > > "a > > > while" actually was. > > > > This macvtap zero copy uses iov buffers from vhost ring, which is > > allocated from guest kernel. In host kernel, vhost calls macvtap > > sendmsg. macvtap sendmsg calls get_user_pages_fast to pin these buffers' > > pages for zero copy. > > > > The patch is relying on how vhost handle these buffers. I need to look > > at vhost code (qemu) first for addressing the questions here. > > I guess the best solution would be to make macvtap_aio_write return > -EIOCBQUEUED when a packet gets passed down to the adapter, and > call aio_complete when the adapter is done with it. > > This would change the regular behavior of macvtap into a model where > every write on the file blocks until the packet has left the machine, > which gives us better flow control, but does slow down the traffic > when we only put one packet at a time into the queue. > > It also allows the user to call io_submit instead of write in order > to do an asynchronous submission as Avi was suggesting. > > Arnd I would expect this to hurt performance significantly. We could do this for asynchronous requests only to avoid the slowdown. -- MST -- 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
