From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Joerg Roedel" Subject: Re: paravirtualization & cr3-cache feature Date: Mon, 12 Feb 2007 14:06:44 +0100 Message-ID: <20070212130644.GF25460@amd.com> References: <64F9B87B6B770947A9F8391472E032160A66BE0A@ehost011-8.exch011.intermedia.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: "Dor Laor" Return-path: In-Reply-To: <64F9B87B6B770947A9F8391472E032160A66BE0A-yEcIvxbTEBqsx+V+t5oei8rau4O3wl8o3fe8/T/H7NteoWH0uzbU5w@public.gmane.org> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Sat, Feb 10, 2007 at 02:22:25PM -0800, Dor Laor wrote: > > >hi, > > Can someone briefly explain what the cr3-cache feature on intel VT > >processors is and how it is used to improve performance in > >paravirtualization. > > In short, this is a unique Intel VT feature that supposed to save vmexit > on cr3 switch. The vmexit operation is quite expensive at the moment > (something like 2-5 ms!). PV kernels can use this feature by sharing ^^^^^^^^^^^^^^^^^^^^^^^^ Where do you measured this unbelievable large number? On AMD-V I measured around 2400 processor cycles for a VMEXIT/VMENTRY roundtrip. I would really really wonder if Intel-VT is that slow... Joerg -- Joerg Roedel Operating System Research Center AMD Saxony LLC & Co. KG ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier. Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642