From mboxrd@z Thu Jan 1 00:00:00 1970 From: Muli Ben-Yehuda Subject: Re: VT-d support for device assignment Date: Fri, 22 Aug 2008 22:09:17 +0300 Message-ID: <20080822190917.GK6885@il.ibm.com> References: <1219389054-15332-1-git-send-email-amit.shah@qumranet.com> <200808222102.33596.amit.shah@qumranet.com> <20080822182948.GJ6885@il.ibm.com> <48AF075C.7050904@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Amit Shah , Byron Stanoszek , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mtagate2.de.ibm.com ([195.212.17.162]:42960 "EHLO mtagate2.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756040AbYHVTJ1 (ORCPT ); Fri, 22 Aug 2008 15:09:27 -0400 Received: from d12nrmr1607.megacenter.de.ibm.com (d12nrmr1607.megacenter.de.ibm.com [9.149.167.49]) by mtagate2.de.ibm.com (8.13.1/8.13.1) with ESMTP id m7MJ9PnO005730 for ; Fri, 22 Aug 2008 19:09:25 GMT Received: from d12av04.megacenter.de.ibm.com (d12av04.megacenter.de.ibm.com [9.149.165.229]) by d12nrmr1607.megacenter.de.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m7MJ9PKL3088606 for ; Fri, 22 Aug 2008 21:09:25 +0200 Received: from d12av04.megacenter.de.ibm.com (loopback [127.0.0.1]) by d12av04.megacenter.de.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m7MJ9Lbk015761 for ; Fri, 22 Aug 2008 21:09:22 +0200 Content-Disposition: inline In-Reply-To: <48AF075C.7050904@qumranet.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Aug 22, 2008 at 09:37:16PM +0300, Avi Kivity wrote: > > Actually, with direct-mmio we bypass QEMU and get a nice boost in > > performance, and it should be possible to bypass QEMU for (most) > > PIO's too. > > Since there is no pio remapping, there's no way to ensure there's a > free pio range where the guest maps its ports. True, and we also need to trap pio's for things like configuration space accesses that the host needs to know about, such as BAR re-mappings. Hence my (parenthetical) comment with regards to "most". It's not at all clear that the gain will be worth the complexity to decide which pio's to trap and which to let through directly. Cheers, Muli -- Workshop on I/O Virtualization (WIOV '08) Co-located with OSDI '08, Dec 2008, San Diego, CA http://www.usenix.org/wiov08