From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: macvtap performance regression (bisected) between 3.13 and 3.14-rc1 Date: Sat, 01 Mar 2014 14:27:17 -0500 Message-ID: <53123495.7030902@gmail.com> References: <530FA586.3010400@de.ibm.com> <53110A62.7070109@redhat.com> <5311C142.6040509@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Jason Wang , "Michael S. Tsirkin" , netdev@vger.kernel.org, KVM list , Linux Kernel Mailing List To: Christian Borntraeger , vyasevic@redhat.com Return-path: Received: from mail-qc0-f180.google.com ([209.85.216.180]:33492 "EHLO mail-qc0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753194AbaCAT1V (ORCPT ); Sat, 1 Mar 2014 14:27:21 -0500 In-Reply-To: <5311C142.6040509@de.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 > > 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 >