From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756584AbZEUXLz (ORCPT ); Thu, 21 May 2009 19:11:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756250AbZEUXLh (ORCPT ); Thu, 21 May 2009 19:11:37 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48817 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755971AbZEUXLg (ORCPT ); Thu, 21 May 2009 19:11:36 -0400 Message-ID: <4A15DF4E.6060209@zytor.com> Date: Thu, 21 May 2009 16:10:06 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Chuck Ebbert , Ingo Molnar , "Xin, Xiaohui" , "Li, Xin" , "Nakajima, Jun" , Nick Piggin , Linux Kernel Mailing List , Xen-devel Subject: Re: Performance overhead of paravirt_ops on native identified References: <4A0B62F7.5030802@goop.org> <20090521184233.3c3e97ad@dhcp-100-2-144.bos.redhat.com> <4A15DA4E.2090505@goop.org> In-Reply-To: <4A15DA4E.2090505@goop.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeremy Fitzhardinge wrote: > > In this specific instance of this example, yes. But if you start > enabling various spinlock debug options then there'll be code following > the call. It would be hard for the runtime patching machinery to know > when it would be safe to do the substitution. > "When it is immediately followed by a ret" seems like a straightforward rule to me? -hpa