Subject: Re: Regression: too many packets with incorrect checksum

From: Cong Wang <[email-masked]>
Date: Thu, 09 May 2013 17:17:43 +0800

On Thu, 2013-05-09 at 16:36 +0800, Cong Wang wrote:
> 
> Running another RHEL6 KVM guest, it doesn't have this problem, so it is
> not related with KVM environment.

I thought it might be due to tcpdump receives a packet which is
checksummed partially while the wire receives a correct one, but netperf
shows that is wrong, apparently it hurts performance:

With latest -net:

~% netperf -4 -H 192.168.122.74
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.122.74 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.20     105.19

With a RHEL6 kernel:

~% netperf -4 -H 192.168.122.101
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.122.101 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    5528.64