From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45329) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1awqY3-0007ie-Tr for qemu-devel@nongnu.org; Sun, 01 May 2016 08:32:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1awqXs-0001hM-9z for qemu-devel@nongnu.org; Sun, 01 May 2016 08:32:26 -0400 Received: from mailout.ish.de ([80.69.98.247]:44672) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1awqXs-0001cO-3z for qemu-devel@nongnu.org; Sun, 01 May 2016 08:32:20 -0400 Received: from submit.unitybox.de (submit.unitybox.de [80.69.98.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mailout.ish.de (Postfix) with ESMTPS id 3qyRXX4pnsz7ZKFx for ; Sun, 1 May 2016 14:27:40 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by submit.unitybox.de (Postfix) with ESMTP id 3qyRdX4ZqVz7t93 for ; Sun, 1 May 2016 14:32:00 +0200 (CEST) Received: from submit.unitybox.de ([127.0.0.1]) by localhost (submit.unitybox.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id Kb0NMrWBezxJ for ; Sun, 1 May 2016 14:32:00 +0200 (CEST) Received: from laptop.ikrabbe-ask.de (ip-178-200-234-99.hsi07.unitymediagroup.de [178.200.234.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by submit.unitybox.de (Postfix) with ESMTPSA id 3qyRdX3BfGz7t8X for ; Sun, 1 May 2016 14:31:59 +0200 (CEST) Received: from krabbe.protel.vpn (unknown [192.168.122.136]) by laptop.ikrabbe-ask.de (Postfix) with ESMTP id 4D2ECE02A1 for ; Sun, 1 May 2016 14:31:58 +0200 (CEST) Message-ID: <404102019afadcf28f8dcb958fcbf617@yourdomain.dom> Date: Sun, 1 May 2016 14:31:57 +0200 From: Ingo Krabbe MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] TCP Segementation Offloading List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Good Mayday Qemu Developers, today I tried to find a reference to a networking problem, that seems to be of quite general nature: TCP Segmentation Offloading (TSO) in virtual environments. When I setup TAP network adapter for a virtual machine and put it into a host bridge, the known best practice is to manually set "tso off gso off" with ethtool, for the guest driver if I use a hardware emulation, such as e1000 and/or "tso off gso off" for the host driver and/or for the bridge adapter, if I use the virtio driver, as otherwise you experience (sometimes?) performance problems or even lost packages. I haven't found a complete analysis of the background of these problems, but there seem to be some effects on MTU based fragmentation and UDP checksums. There is a tso related bug on launchpad, but the context of this bug is too narrow, for the generality of the problem. Also it seems that there is a problem in LXC contexts too (I found such a reference, without detailed description in a Post about Xen setup). My question now is: Is there a bug in the driver code and shouldn't this be documented somewhere in wiki.qemu.org? Where there developments about this topic in the past or is there any planned/ongoing work todo on the qemu drivers? Most problem reports found relate to deprecated Centos6 qemu-kvm packages. In our company we have similar or even worse problems with Centos7 hosts and guest machines. I'm going to analyze these problems next week anyway and I woud be happy to share my observation with you. (Where can I register for the wiki, or whom should I sent my reports about this topic?). Regards, Ingo Krabbe