From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753525AbaCBB2l (ORCPT ); Sat, 1 Mar 2014 20:28:41 -0500 Received: from mail-qc0-f170.google.com ([209.85.216.170]:36067 "EHLO mail-qc0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753367AbaCBB2j (ORCPT ); Sat, 1 Mar 2014 20:28:39 -0500 Message-ID: <531287AE.5080606@gmail.com> Date: Sat, 01 Mar 2014 20:21:50 -0500 From: Vlad Yasevich User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Christian Borntraeger , vyasevic@redhat.com CC: "David S. Miller" , Jason Wang , "Michael S. Tsirkin" , netdev@vger.kernel.org, KVM list , Linux Kernel Mailing List Subject: Re: macvtap performance regression (bisected) between 3.13 and 3.14-rc1 References: <530FA586.3010400@de.ibm.com> <53110A62.7070109@redhat.com> <5311C142.6040509@de.ibm.com> <53123495.7030902@gmail.com> In-Reply-To: <53123495.7030902@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/01/2014 02:27 PM, Vlad Yasevich wrote: > On 03/01/2014 06:15 AM, Christian Borntraeger wrote: >> On 28/02/14 23:14, Vlad Yasevich wrote: >>> On 02/27/2014 03:52 PM, Christian Borntraeger wrote: >>>> Vlad, >>>> >>>> commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 >>>> macvtap: Add support of packet capture on macvtap device. >>>> >>>> causes a performance regression for iperf traffic between two KVM guests >>>> on my s390 system. Both guests are connected via two macvtaps on the same OSA >>>> network card. >>>> Before that patch I get ~20 Gbit/sec between two guests, afterwards I get >>>> ~4Gbit/sec >>>> >>>> Latency seems to be unchanges (uperf 1byte ping pong). >>>> >>>> According to ifconfig in the guest, I have ~ 1500 bytes per packet with this >>>> patch and ~ 40000 bytes without. So for some reason this patch causes the >>>> network stack to do segmentation. (the guest kernel stays the same, only host >>>> kernel is changed). >>>> >>>> Any ideas? >>> >>> I am looking. It shouldn't cause addition segmentations and when I ran >>> netperf on the code I didn't see any difference in the throughput. >> >> Dont know if the different bytes/packets ratio is really the reason or >> just a side effect. As a hint: the underlying network device does not support >> segmentation, but this should not matter for traffic between to guests. > > Could you post 'ethtool -k' output for both lower-level device and the > macvtap device? > > Thanks > -vlad > Ok. I think I see what's happening. Since you turn off offloads on lower device, that's propagated to macvlan device. As a result, when when we call dev_queue_xmit on the vlan->dev, we end up segmenting since lower level says it does support segmentation. One way to fix this is to never disable offloads on macvlan. macvlan will always try to use __dev_queue_xmit() with it's lower device, so any segmentation can happen there. -vlad >> >> Maybe you remember, we had a similar situation with commit 3e4f8b787370978733ca6cae452720a4f0c296b8 >> (macvtap: Perform GSO on forwarding path), the setup is basically the same. >> >> >> Christian >> >> -- >> 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 >> >