From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932172AbcA0MTK (ORCPT ); Wed, 27 Jan 2016 07:19:10 -0500 Received: from verein.lst.de ([213.95.11.211]:40910 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbcA0MTI (ORCPT ); Wed, 27 Jan 2016 07:19:08 -0500 Date: Wed, 27 Jan 2016 13:19:04 +0100 From: Torsten Duwe To: Balbir Singh Cc: Steven Rostedt , Michael Ellerman , Jiri Kosina , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH v6 0/9] ftrace with regs + live patching for ppc64 LE (ABI v2) Message-ID: <20160127121904.GB32095@lst.de> References: <20160125170459.14DB7692CE@newverein.lst.de> <20160127215112.080eec56@cotter.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160127215112.080eec56@cotter.ozlabs.ibm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 27, 2016 at 09:51:12PM +1100, Balbir Singh wrote: > On Mon, 25 Jan 2016 16:38:48 +0100 > Torsten Duwe wrote: > > > Changes since v5: > > * extra "std r0,LRSAVE(r1)" for gcc-6 > > This makes the code compiler-agnostic. > > * Follow Petr Mladek's suggestion to avoid > > redefinition of HAVE_LIVEPATCH > > I looked at the patches - well mostly patches 1 and 2, some quick questions > > 1. I know -mprofile-kernel is a big optimization win, do we need it or can > we incrementally add it? There's a reason why these are first ;-) The following ones assume -mprofile-kernel is used. The disadvantage is all relevant registers need to be saved before calling further C code in between functions. On the Pro side, no stack frame has been created at that point. These are assumptions made all over the ftrace-with-regs and live patching code here. > 2. Some of the hardcoded checks for opcode are hard to review, I know they've > been there in similar forms for a while. May be as an iterative step we should > give the numbers some meaning and use proper helpers for it. Yes, Michael has already criticised that. No further literal hex constants, I promise. > I am going to give the patches a spin Thanks! Make sure you use a compiler that can disable -mprofile-kernel with "notrace". Torsten