From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:44433) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RoMos-0004Dk-R2 for qemu-devel@nongnu.org; Fri, 20 Jan 2012 17:20:27 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RoMor-00064Z-Vd for qemu-devel@nongnu.org; Fri, 20 Jan 2012 17:20:26 -0500 Received: from lo.gmane.org ([80.91.229.12]:34731) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RoMor-00064M-L9 for qemu-devel@nongnu.org; Fri, 20 Jan 2012 17:20:25 -0500 Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1RoMop-0001ox-Sr for qemu-devel@nongnu.org; Fri, 20 Jan 2012 23:20:23 +0100 Received: from barriere.frankfurter-softwarefabrik.de ([217.11.197.1]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 20 Jan 2012 23:20:23 +0100 Received: from lvml by barriere.frankfurter-softwarefabrik.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 20 Jan 2012 23:20:23 +0100 From: Lutz Vieweg Date: Fri, 20 Jan 2012 23:20:11 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit In-Reply-To: Subject: Re: [Qemu-devel] macvtap performance: good when writing from guest, abysmal when reading on guest (~ 700kB/s) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Adding to my symptom description: I re-tested with "vhost=on" in addition and verified this feature was actually used. But this didn't change the benchmark results. Regards, Lutz Vieweg On 01/20/2012 04:10 PM, Lutz Vieweg wrote: > Hi, > > I've been using qemu-kvm along with ordinary tap-devices and software bridges > for quite some time. When I recently noticed that a certain TCP connection between > a guest and a remote physical host was limited to ~ 80MB/s, I thought it would > be a good idea to check whether by using "macvtap", instead, the performance > would get better. > > So I setup a guest on a host that has a direct peer-to-peer 10G cable to > another host, and configured it to use a macvtap device. > > Then I did some benchmarks, using "nc" on both sides, just reading from /dev/zero, > writing to /dev/null. > > When the guest VM is writing into a TCP connection to the physical host (linux-3.1.6), > the performance is ~ 140MB/s - not great, but better than with ordinary > tap devices. > > But to my big surprise, the performance when the physical host is writing, > and the guest VM is reading is abysmal, only ~ 700kB/s! > No bottleneck is obvious - the CPU usage and NIC utilization of both > the VM, its host, and the other host is all quite low. > "strace" on qemu process indicates that from time to time, there are "pauses" of ~ 0.5 > seconds in between the many reads from /dev/tapX, but I am not sure whether > this is the whole reason for the bad performance. > > Any ideas? > > Or should I rather stay with ordinary tap/brctl, or try yet another > virtual NIC technique? > > Regards, > > Lutz Vieweg > > > >