From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: kvm network latency, higher with virtio ? Date: Wed, 16 Sep 2009 10:27:31 +0300 Message-ID: <20090916072731.GA28995@redhat.com> References: <20090915151509.GC22518@esaurito.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org To: Luca Bigliardi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46306 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752181AbZIPH3f (ORCPT ); Wed, 16 Sep 2009 03:29:35 -0400 Content-Disposition: inline In-Reply-To: <20090915151509.GC22518@esaurito.net> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Sep 15, 2009 at 05:15:09PM +0200, Luca Bigliardi wrote: > Hi, > I'm running some tests between two linux instances bridged together. > > If I try to ping 10 times I obtain the following results: > > -net nic,model=virtio -net tap : > rtt min/avg/max/mdev = 0.756/0.967/2.115/0.389 ms > > -net nic,model=rtl8139 -net tap : > rtt min/avg/max/mdev = 0.301/0.449/1.173/0.248 ms > > So it seems with virtio the latency is higher. Is it normal? Yes, the main reason is the TX timer it uses for interrupt/vm exit mitigation. > The results I'm reporting were obtained with > - host > qemu-kvm 0.11-rc2 > kvm-kmod-2.6.30.1 > kernel: 2.6.30.5 (HIGH_RES_TIMERS=y as suggested in > http://www.linux-kvm.org/page/Virtio ) > - guest > kernel: 2.6.31 > > but I also tested older versions always obtaining latency values at least two > times higher than rtl8139/e1000 . > > Thank you, > Luca > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html