From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bernhard Schmidt Subject: Re: virtio performance issue Date: Tue, 16 Sep 2008 17:43:15 +0000 (UTC) Message-ID: References: <1221574441.26630.19.camel@cluwyn.haifa.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit To: kvm@vger.kernel.org Return-path: Received: from main.gmane.org ([80.91.229.2]:36830 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754487AbYIPRnZ (ORCPT ); Tue, 16 Sep 2008 13:43:25 -0400 Received: from list by ciao.gmane.org with local (Exim 4.43) id 1KfeaC-0002Dg-01 for kvm@vger.kernel.org; Tue, 16 Sep 2008 17:43:24 +0000 Received: from ppp-88-217-20-11.dynamic.mnet-online.de ([88.217.20.11]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 16 Sep 2008 17:43:23 +0000 Received: from berni by ppp-88-217-20-11.dynamic.mnet-online.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 16 Sep 2008 17:43:23 +0000 Sender: kvm-owner@vger.kernel.org List-ID: Ben-Ami Yassour wrote: Hello Ben, > I am running virtio with the latest KVM code, and see a significant > performance issue. > > Ping to the host (or any other close machine) reports a 4ms delay. > > In the same setup with an e1000 emulation (just changing model=virtio to > model=e1000 in the KVM command line), ping reports 0.177ms delay. > > BTW, initially I saw that the throughput when using netperf is very low, > even from guest to host, even though the CPU utilization is low. > > What might be the problem? I had exactly the same issue (with an 2.6.26 kernel and kvm-70 though). In an attempt to make the guest kernel (w/o modules) as small as possible I had disabled ACPI in its config. Which works, but introduced the very same 4ms delay you are seeing and made the VM clock go wild (even worse with KVM_CLOCK). I did not see other speed issues, but I have to admit I never benchmarked it. After enabling ACPI the 4ms delay baseline disappeared and the clock in the guest is now perfectly in sync with the host. Regards, Bernhard