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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is written
Date: Mon, 27 May 2013 10:32:25 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

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
>           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.

> 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 still reproduce the problem now that the patch has been merged
into qemu.git/master?


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