Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756832AbXHVGAr (ORCPT ); Wed, 22 Aug 2007 02:00:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754173AbXHVGAk (ORCPT ); Wed, 22 Aug 2007 02:00:40 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34698 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753906AbXHVGAj (ORCPT ); Wed, 22 Aug 2007 02:00:39 -0400 Message-ID: <46CBD0F5.2080709@zytor.com> Date: Tue, 21 Aug 2007 23:00:21 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.0 (X11/20070419) MIME-Version: 1.0 To: Zachary Amsden CC: Andrew Morton , Linux Kernel Mailing List , Virtualization Mailing List , Rusty Russell , Chris Wright , Avi Kivity , Jeremy Fitzhardinge Subject: Re: [PATCH] Add I/O hypercalls for i386 paravirt References: <46CBC842.4070100@vmware.com> In-Reply-To: <46CBC842.4070100@vmware.com> X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1264 Lines: 26 Zachary Amsden wrote: > In general, I/O in a virtual guest is subject to performance problems. > The I/O can not be completed physically, but must be virtualized. This > means trapping and decoding port I/O instructions from the guest OS. > Not only is the trap for a #GP heavyweight, both in the processor and > the hypervisor (which usually has a complex #GP path), but this forces > the hypervisor to decode the individual instruction which has faulted. > Worse, even with hardware assist such as VT, the exit reason alone is > not sufficient to determine the true nature of the faulting instruction, > requiring a complex and costly instruction decode and simulation. > > This patch provides hypercalls for the i386 port I/O instructions, which > vastly helps guests which use native-style drivers. For certain VMI > workloads, this provides a performance boost of up to 30%. We expect > KVM and lguest to be able to achieve similar gains on I/O intensive > workloads. > What about cost on hardware? -hpa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/