On Thu, Aug 30, 2012 at 09:20:57AM +0100, Richard Davies wrote:

Chris Webb wrote:

quoted

I found that on my laptop, the single change of host kernel config

-CONFIG_INTEL_IDLE=y
+# CONFIG_INTEL_IDLE is not set

is sufficient to turn transfers into guests from slow to full wire speed

I am not deep enough in this code to write a patch, but I wonder if
macvtap_forward in macvtap.c is missing a call to kill_fasync, which I
understand is used to signal to interested processes when data arrives?

No, only if TUN_FASYNC is set. qemu does not seem to set it.

Here is the end of macvtap_forward:

  skb_queue_tail(&q->sk.sk_receive_queue, skb);
  wake_up_interruptible_poll(sk_sleep(&q->sk), POLLIN | POLLRDNORM | POLLRDBAND);
  return NET_RX_SUCCESS;


Compared to this end of tun_net_xmit in tun.c:

  /* Enqueue packet */
  skb_queue_tail(&tun->socket.sk->sk_receive_queue, skb);

  /* Notify and wake up reader process */
  if (tun->flags & TUN_FASYNC)
          kill_fasync(&tun->fasync, SIGIO, POLL_IN);
  wake_up_interruptible_poll(&tun->wq.wait, POLLIN |
                             POLLRDNORM | POLLRDBAND);
  return NETDEV_TX_OK;


Richard.