Re: [Xen-devel] vif tx drops

[David Becker <becker@xxxxxxxxxxx>]

" " Please try changing the following line in netfront.c:
" " #define RX_MIN_TARGET 8
" " to:
" " #define RX_MIN_TARGET NETIF_RX_RING_SIZE


It looks like xen0 or the bridge stuff is not getting some packets
destined for xenU.

I traced an ssh connection from a machine running stock 2.4.25
to a xenU domain by running tcpdump on xen0 and on the other machine.

The trace on xen0 shows a 4 second gap where no ssh packets were received
for the xenU domain even though the other machine was sending retransmits. 
Only the last retransmit appears in the xen0 dump.

It is unlikely the network dropped the missing packets.  This is low bandwidth
stuff and somewhat repeatable.  I've never seen the effect on xen0, and
in this case, there is another xenU domain on the same host
showing no pause symptoms.

The 'netstat -i' statistics on xen0 and xenU do not show any dropped packets.


On xen0, tcpdump -i eth0 shows the 4 second gap between packets going to xenU:
13:58:24.247209 IP firefly-batch.39292 > batch009.ssh: . ack 8065 win 40544 
<nop,nop,timestamp 431700765 1532967>
13:58:28.432536 IP firefly-batch.39292 > batch009.ssh: P 1296:1392(96) ack 8065 
win 40544 <nop,nop,timestamp 431701184 1532967>


On the other host tcpdump shows those two packets, plus 5 more
duplicates sent during the gap:
13:58:24.262055 IP firefly-batch.39292 > batch009.ssh: . ack 2145 win 40544 
<nop,nop,timestamp 431700765 1532967>
13:58:25.302477 IP firefly-batch.39292 > batch009.ssh: P 720:768(48) ack 2145 
win 40544 <nop,nop,timestamp 431700869 1532967>
13:58:25.414312 IP firefly-batch.39292 > batch009.ssh: P 768:816(48) ack 2145 
win 40544 <nop,nop,timestamp 431700880 1532967>
13:58:25.507337 IP firefly-batch.39292 > batch009.ssh: P 720:816(96) ack 2145 
win 40544 <nop,nop,timestamp 431700890 1532967>
13:58:25.927331 IP firefly-batch.39292 > batch009.ssh: P 720:816(96) ack 2145 
win 40544 <nop,nop,timestamp 431700932 1532967>
13:58:26.767331 IP firefly-batch.39292 > batch009.ssh: P 720:816(96) ack 2145 
win 40544 <nop,nop,timestamp 431701016 1532967>
13:58:28.447331 IP firefly-batch.39292 > batch009.ssh: P 720:816(96) ack 2145 
win 40544 <nop,nop,timestamp 431701184 1532967>



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