From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: Network packet size over MTU in guests Date: Wed, 07 Oct 2009 15:25:15 +0400 Message-ID: <4ACC7A9B.4080407@msgid.tls.msk.ru> References: <4ACC5364.6010602@openweb.be> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Fabrice Toppi Return-path: Received: from isrv.corpit.ru ([81.13.33.159]:56299 "EHLO isrv.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758983AbZJGLZx (ORCPT ); Wed, 7 Oct 2009 07:25:53 -0400 In-Reply-To: <4ACC5364.6010602@openweb.be> Sender: kvm-owner@vger.kernel.org List-ID: Fabrice Toppi wrote: > Hi, > > We use KVM 75 on Gentoo hosts with kernel 2.6.27.8 with a variety of > guests (Windows XP, 2000, 2003 & several Linux distributions) in a > production setup. > The hosts are Intel Xeon based. We use bridged networking with E1000 > model inside of guests. > > Recently, we began to have network problem (slowdowns, lags, timeouts) > on several guests. Inside those guests, we saw with tcpdump that there > were packets with a size well over MTU. On the host, tcpdump on the > guest tap did show packets of 1500 bytes and that's all. > For some of the guests (Debian based), changing the NIC model to rtl8139 > instead of e1000 "fixed" the problem, but for others (Gentoo kernel > 2.6.27.19) it didn't. > > Would it be a glitch in the KVM code or a driver problem ? Does this > ring a bell to anyone ? I'm not sure anymore but I think it's very similar to what I had here with pre-78 (approx again, since it was quite some time ago) versions of kvm compiled with older kernel headers (without appropriate if_tun.h definitions). I'd say try to reproduce it with 0.11.0 kvm userspace compiled against 2.6.27+ kernel headers. But yet again: kvm-75 is quite old by now, so it's difficult to remember all the details. /mjt