From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754102Ab1A3NCQ (ORCPT ); Sun, 30 Jan 2011 08:02:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38052 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753804Ab1A3NCO (ORCPT ); Sun, 30 Jan 2011 08:02:14 -0500 Message-ID: <4D456139.4090508@redhat.com> Date: Sun, 30 Jan 2011 15:01:45 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.7 MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Jan Beulich , Xiaowei Yang , Nick Piggin , Peter Zijlstra , fanhenglong@huawei.com, Kaushik Barde , Kenneth Lee , linqaingmin , wangzhenguo@huawei.com, Wu Fengguang , "xen-devel@lists.xensource.com" , linux-kernel@vger.kernel.org, Marcelo Tosatti Subject: Re: One (possible) x86 get_user_pages bug References: <4D416D9A.9010603@huawei.com> <4D419416020000780002ECB7@vpn.id2.novell.com> <4D41B90D.5000305@goop.org> In-Reply-To: <4D41B90D.5000305@goop.org> 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 On 01/27/2011 08:27 PM, Jeremy Fitzhardinge wrote: > And even just considering virtualization, having non-IPI-based tlb > shootdown is a measurable performance win, since a hypervisor can > optimise away a cross-VCPU shootdown if it knows no physical TLB > contains the target VCPU's entries. I can imagine the KVM folks could > get some benefit from that as well. It's nice to avoid the IPI (and waking up a cpu if it happens to be asleep) but I think the risk of deviating too much from the baremetal arch is too large, as demonstrated by this bug. (well, async page faults is a counterexample, I wonder if/when it will bite us) -- error compiling committee.c: too many arguments to function