From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: FAQ on linux-kvm.org has broken link
Date: Fri, 1 Nov 2013 10:52:03 +0100
Message-ID: <20131101095203.GE17709@stefanha-thinkpad.redhat.com>
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Cc: kvm <kvm@vger.kernel.org>, Christian Theune <ct@gocept.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>
To: folkert <folkert@vanheusden.com>
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On Tue, Oct 29, 2013 at 06:18:05PM +0100, folkert wrote:
> > > > 2. Get the system into the bad state and then do some deeper.  Start
> > > >    with outgoing ping, instrument guest driver and host vhost_net
> > > >    functions to see what the drivers are doing, inspect the transmit
> > > >    vring, etc.
> 
> Update: have not gotten around to reboot the server for the new kernel
> with those probes, but: it is definately very much worse on tuesday(!)
> and when I use mosh to remotely login.

If you're hitting the oversized GSO packet issue that Christian Theune
also seems to be hitting, then further debugging isn't necessary on your
part.

When guest network tx is stalled, please check the following on the
host:

  (host)# ifconfig vnet0
  vnet0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
          inet 192.168.122.123  netmask 255.255.255.0  broadcast 192.168.122.255
          ether 52:54:00:bb:01:ac  txqueuelen 0  (Ethernet)
          RX packets 0  bytes 0 (0.0 B)
          RX errors 0  dropped 1  overruns 0  frame 0
          TX packets 0  bytes 0 (0.0 B)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

If you see "RX dropped" greater than zero then it's probably the same issue.

Stefan