Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755913AbYKQBrS (ORCPT ); Sun, 16 Nov 2008 20:47:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754567AbYKQBrA (ORCPT ); Sun, 16 Nov 2008 20:47:00 -0500 Received: from mga09.intel.com ([134.134.136.24]:47395 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753824AbYKQBq7 (ORCPT ); Sun, 16 Nov 2008 20:46:59 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.33,615,1220252400"; d="scan'208";a="463801660" Message-ID: <4920CD0F.8070107@intel.com> Date: Mon, 17 Nov 2008 09:46:55 +0800 From: "Zhao, Yu" User-Agent: Thunderbird 2.0.0.17 (Windows/20080914) MIME-Version: 1.0 To: Avi Kivity CC: Anthony Liguori , Andi Kleen , "randy.dunlap@oracle.com" , "grundler@parisc-linux.org" , "Chiang, Alexander" , Matthew Wilcox , Greg KH , "rdreier@cisco.com" , "linux-kernel@vger.kernel.org" , "jbarnes@virtuousgeek.org" , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" , "mingo@elte.hu" Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support References: <20081106154351.GA30459@kroah.com> <894107.30288.qm@web45108.mail.sp1.yahoo.com> <20081106164919.GA4099@kroah.com> <0199E0D51A61344794750DC57738F58E5E26F996C4@GVW1118EXC.americas.hpqcorp.net> <20081106183630.GD11773@parisc-linux.org> <491371F0.7020805@codemonkey.ws> <87d4h7pnnm.fsf__4937.77150190926$1226071173$gmane$org@basil.nowhere.org> <491B5B97.2000407@codemonkey.ws> <492044A7.3080107@redhat.com> In-Reply-To: <492044A7.3080107@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1262 Lines: 29 Avi Kivity wrote: > Anthony Liguori wrote: >> I don't think it's established that PV/VF will have less latency than >> using virtio-net. virtio-net requires a world switch to send a group >> of packets. The cost of this (if it stays in kernel) is only a few >> thousand cycles on the most modern processors. >> >> Using VT-d means that for every DMA fetch that misses in the IOTLB, >> you potentially have to do four memory fetches to main memory. There >> will be additional packet latency using VT-d compared to native, it's >> just not known how much at this time. > > If the IOTLB has intermediate TLB entries like the processor, we're > talking just one or two fetches. That's a lot less than the cacheline > bouncing that virtio and kvm interrupt injection incur right now. > The PCI SIG Address Translation Service (ATS) specifies a way that uses an Address Translation Cache (ATC) in the Endpoint to reduce the latency. The Linux kernel support for ATS capability will come soon. Thanks, Yu -- 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/