Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757233AbXH1GuQ (ORCPT ); Tue, 28 Aug 2007 02:50:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754658AbXH1GuA (ORCPT ); Tue, 28 Aug 2007 02:50:00 -0400 Received: from gate.crashing.org ([63.228.1.57]:53420 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751333AbXH1Gt7 (ORCPT ); Tue, 28 Aug 2007 02:49:59 -0400 Subject: Re: [PATCH] Add I/O hypercalls for i386 paravirt From: Benjamin Herrenschmidt To: Zachary Amsden Cc: Andrew Morton , Linux Kernel Mailing List , Virtualization Mailing List , Rusty Russell , Chris Wright , Avi Kivity , Jeremy Fitzhardinge In-Reply-To: <46CBC842.4070100@vmware.com> References: <46CBC842.4070100@vmware.com> Content-Type: text/plain Date: Mon, 27 Aug 2007 19:54:13 +0200 Message-Id: <1188237253.5972.67.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1091 Lines: 24 On Tue, 2007-08-21 at 22:23 -0700, 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. .../... How about userland ? Things like X do IO's typically... You still need to trap/emulate for these no ? Cheers, Ben. - 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/