Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is written

[Peter Lieven]

On 27.05.2013 10:32, Stefan Hajnoczi wrote:
> On Mon, May 27, 2013 at 08:15:42AM +0200, Peter Lieven wrote:
> > I ocassionally have seen a probably related problem in the past. It mainly 
> > happend with rtl8139 under
> > WinXP where we most likely use rtl8139 due to lack of shipped e1000 drivers.
> >
> > My question is if you see increasing dropped packets on the tap device if this 
> > problem occurs?
> >
> > tap36     Link encap:Ethernet  HWaddr b2:84:23:c0:e2:c0
> >            inet6 addr: fe80::b084:23ff:fec0:e2c0/64 Scope:Link
> >            UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
> >            RX packets:5816096 errors:0 dropped:0 overruns:0 frame:0
> >            TX packets:3878744 errors:0 dropped:13775 overruns:0 carrier:0
> >            collisions:0 txqueuelen:500
> >            RX bytes:5161769434 (5.1 GB)  TX bytes:380415916 (380.4 MB)
> My reading of the tun code is that will see TX dropped increase.  This
> is because tun keeps a finite size queue of tx packets.  Since QEMU
> userspace is not monitoring the tap fd anymore we'll never drain the
> queue and soon enough the TX dropped counter will begin incrementing.
Ok, so this would fit.

> > In my case as well the only option to recover without shutting down the whole 
> > vServer is Live Migration
> > to another Node.
> >
> > However, I also see this problem under qemu-kvm-1.2.0 while Oliver reported it 
> > does not happen there.
> Yes, the patch that exposes this problem was only merged in 1.2.1.
Can you say which patch exactly? I cherry-picked some patches by hand.
> Can you still reproduce the problem now that the patch has been merged
> into qemu.git/master?
Unfortunately, I have no reliable way of reproducing the issue. It only happens
from time to time.

Peter