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Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is
Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is written
Mon, 27 May 2013 16:07:53 +0200
Am 27.05.2013 um 08:15 schrieb Peter Lieven <address@hidden>:
> Hi all,
> 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)
> In my case as well the only option to recover without shutting down the whole
> vServer is Live Migration
> to another Node.
ACK, tried it and every network-devices might have been re-created into a
defined state qemu-wise.
> However, I also see this problem under qemu-kvm-1.2.0 while Oliver reported
> it does not happen there.
Neither me nor any affected customers have ever seen such failures in
qemu-1.2.0, so this was my last-known-good ;)
> Thank you,
> On 22.05.2013 14:50, Stefan Hajnoczi wrote:
>> Net queues support efficient "receive disable". For example, tap's file
>> descriptor will not be polled while its peer has receive disabled. This
>> saves CPU cycles for needlessly copying and then dropping packets which
>> the peer cannot receive.
>> rtl8139 is missing the qemu_flush_queued_packets() call that wakes the
>> queue up when receive becomes possible again.
>> As a result, the Windows 7 guest driver reaches a state where the
>> rtl8139 cannot receive packets. The driver has actually refilled the
>> receive buffer but we never resume reception.
>> The bug can be reproduced by running a large FTP 'get' inside a Windows
>> 7 guest:
>> $ qemu -netdev tap,id=tap0,...
>> -device rtl8139,netdev=tap0
>> The Linux guest driver does not trigger the bug, probably due to a
>> different buffer management strategy.
>> Reported-by: Oliver Francke <address@hidden>
>> Signed-off-by: Stefan Hajnoczi <address@hidden>
>> hw/net/rtl8139.c | 3 +++
>> 1 file changed, 3 insertions(+)
>> diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
>> index 9369507..7993f9f 100644
>> --- a/hw/net/rtl8139.c
>> +++ b/hw/net/rtl8139.c
>> @@ -2575,6 +2575,9 @@ static void rtl8139_RxBufPtr_write(RTL8139State *s,
>> uint32_t val)
>> /* this value is off by 16 */
>> s->RxBufPtr = MOD2(val + 0x10, s->RxBufferSize);
>> + /* more buffer space may be available so try to receive */
>> + qemu_flush_queued_packets(qemu_get_queue(s->nic));
>> DPRINTF(" CAPR write: rx buffer length %d head 0x%04x read 0x%04x\n",
>> s->RxBufferSize, s->RxBufAddr, s->RxBufPtr);