From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752701AbaCALP3 (ORCPT ); Sat, 1 Mar 2014 06:15:29 -0500 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:52096 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752460AbaCALP1 (ORCPT ); Sat, 1 Mar 2014 06:15:27 -0500 Message-ID: <5311C142.6040509@de.ibm.com> Date: Sat, 01 Mar 2014 12:15:14 +0100 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: 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> In-Reply-To: <53110A62.7070109@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14030111-3548-0000-0000-00000841418E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Maybe you remember, we had a similar situation with commit 3e4f8b787370978733ca6cae452720a4f0c296b8 (macvtap: Perform GSO on forwarding path), the setup is basically the same. Christian