From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: Regression: too many packets with incorrect checksum Date: Thu, 09 May 2013 09:25:31 -0700 Message-ID: <518BCDFB.4090004@hp.com> References: <1368013888.3115.9.camel@cr0> <1368088578.12413.4.camel@cr0> <1368091063.12413.9.camel@cr0> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, "David S. Miller" To: Cong Wang Return-path: Received: from g4t0014.houston.hp.com ([15.201.24.17]:28964 "EHLO g4t0014.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752662Ab3EIQZd (ORCPT ); Thu, 9 May 2013 12:25:33 -0400 In-Reply-To: <1368091063.12413.9.camel@cr0> Sender: netdev-owner@vger.kernel.org List-ID: On 05/09/2013 02:17 AM, Cong Wang wrote: > 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 That the test ran 200 milliseconds "long" (in a LAN environment and compared to the other kernel) is another clue that things were not entirely well. I suspect that were you to have netperf emit local_transport_retrans: netperf -4 -H 192.168.122.74 -- -o throughput,elapsed_time,local_transport_retrans you would see a non-trivial number of retransmissions on the connection. You've no doubt already seen that in netstat -s, but the per-connection stuff netperf can emit can be helpful when there are other things going-on on the system at the same time. happy benchmarking, rick ones > > > 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 > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >