From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chegu Vinod Subject: Re: Networking performance on a KVM Host (with no guests) Date: Fri, 20 Apr 2012 07:15:50 -0700 Message-ID: <4F916F96.8070100@hp.com> References: <20120419054306.GV11918@redhat.com> Reply-To: chegu_vinod@hp.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from g4t0015.houston.hp.com ([15.201.24.18]:43246 "EHLO g4t0015.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756303Ab2DTOQX (ORCPT ); Fri, 20 Apr 2012 10:16:23 -0400 In-Reply-To: <20120419054306.GV11918@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 4/18/2012 10:43 PM, Gleb Natapov wrote: > On Thu, Apr 19, 2012 at 03:53:39AM +0000, Chegu Vinod wrote: >> Hello, >> >> Perhaps this query was answered in the past. If yes kindly point me to >> the same. >> >> We noticed differences in networking performance (measured via netperf >> over a 10G NIC) on an X86_64 server between the following two >> configurations : >> >> 1) Server run as a KVM Host (but with no KVM guests created on it (or) no >> extra bridges created other than the default vibr0 bridge) >> >> vs. >> >> 2) The same server running the same version of Linux but without any of the >> virtualization software installed on it. >> >> Config #2 performed much better ! >> Is this expected ? What are the reasons behind this ? >> >> Is there any way to gain back the loss in performance on the KVM host >> without having to uninstall the virtualization software (i.e. in Config 1). >> >> Just an observation : Removing the "intel_iommu=on" boot time parameter in the Config 1 case seemed to help gain back the networking performance on the KVM host... i.e. performed nearly the same as in Config2. Didn't have to change any of the VT settings in the BIOS... Trying to understand why that's the case... Any pointers ? Vinod > -- > Gleb. >