From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: user space virtio-net exits with "truncating packet" error Date: Fri, 15 May 2009 11:07:43 +0400 Message-ID: <4A0D14BF.5010409@msgid.tls.msk.ru> References: <200905142128.58111.rusty@rustcorp.com.au> <4A0C2500.7090709@Voltaire.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Rusty Russell , Avi Kivity , netdev@vger.kernel.org, Gregory Haskins , Anthony Liguori To: Or Gerlitz Return-path: Received: from isrv.corpit.ru ([81.13.33.159]:49361 "EHLO isrv.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754942AbZEOHHq (ORCPT ); Fri, 15 May 2009 03:07:46 -0400 In-Reply-To: <4A0C2500.7090709@Voltaire.com> Sender: netdev-owner@vger.kernel.org List-ID: Or Gerlitz wrote: > Rusty Russell wrote: >> The answer is that virtio_net by default only supports 1500 >> MTU; I've not tried larger MTUs. > > Rusty, > > I hoped to get some performance boost from using checksum and large-send offloads > as an alternative to jumbo frames. Looking in the virtio-net kernel driver, I see that the probe > function checks if virtio_has_feature VIRTIO_NET_F_CSUM ... VIRTIO_NET_F_HOST_TSO ... and if yes > sets the relevant bits in the NIC features mask. Looking in the virtio qemu code, I also see some offload > related code. A trap which I've seen before. When compiling kvm userspace, ensure your kernel headers installed in /usr/include has the latest if_tun.h bits, in particular the TUNSETOFFLOAD and IFF_VNET_HDR definitions. One solution to this is just to copy that file from kernel-2.6.29. Or maybe it's easier to add some -I flags to kvm compile commandline. And one more note: I'm not sure if there's anything else needed. Last time I was there -- it was with kvm-84 times I think, maybe something changed since that. /mjt