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Re: [Qemu-devel] Slow inbound traffic on macvtap interfaces
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] Slow inbound traffic on macvtap interfaces |
Date: |
Thu, 30 Aug 2012 11:44:33 +0300 |
On Thu, Aug 30, 2012 at 09:20:57AM +0100, Richard Davies wrote:
> Chris Webb wrote:
> > 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.