From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758266AbXIRWH2 (ORCPT ); Tue, 18 Sep 2007 18:07:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754531AbXIRWHV (ORCPT ); Tue, 18 Sep 2007 18:07:21 -0400 Received: from agminet01.oracle.com ([141.146.126.228]:37492 "EHLO agminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754527AbXIRWHT (ORCPT ); Tue, 18 Sep 2007 18:07:19 -0400 Date: Tue, 18 Sep 2007 15:02:32 -0700 From: Randy Dunlap To: Mathieu Desnoyers Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Adrian Bunk , Andi Kleen , Alexey Dobriyan , Christoph Hellwig Subject: Re: [patch 2/7] Immediate Values - Kconfig menu in EMBEDDED Message-Id: <20070918150232.128397b4.randy.dunlap@oracle.com> In-Reply-To: <20070918210852.945316226@polymtl.ca> References: <20070918210747.828804366@polymtl.ca> <20070918210852.945316226@polymtl.ca> Organization: Oracle Linux Eng. X-Mailer: Sylpheed 2.4.2 (GTK+ 2.8.10; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAQAAAAI= X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Sep 2007 17:07:49 -0400 Mathieu Desnoyers wrote: > Immediate values provide a way to use dynamic code patching to update variables > sitting within the instruction stream. It saves caches lines normally used by > static read mostly variables. Enable it by default, but let users disable it > through the EMBEDDED menu with the "Disable immediate values" submenu entry. > > Note: Since I think that I really should let embedded systems developers using > RO memory the option to disable the immediate values, I choose to leave this > menu option there, in the EMBEDDED menu. Also, the "CONFIG_IMMEDIATE" makes > sense because we want to compile out all the immediate code when we decide not > to use optimized immediate values at all (it removes otherwise unused code). > > Signed-off-by: Mathieu Desnoyers > CC: Adrian Bunk > CC: Andi Kleen > CC: Alexey Dobriyan > CC: Christoph Hellwig > --- > init/Kconfig | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > Index: linux-2.6-lttng/init/Kconfig > =================================================================== > --- linux-2.6-lttng.orig/init/Kconfig 2007-09-18 10:09:40.000000000 -0400 > +++ linux-2.6-lttng/init/Kconfig 2007-09-18 13:14:58.000000000 -0400 > @@ -407,6 +407,17 @@ config CC_OPTIMIZE_FOR_SIZE > config SYSCTL > bool > > +config IMMEDIATE > + default y if !DISABLE_IMMEDIATE So DISABLE_IMMEDIATE is just an intermediate symbol to make this option be displayed in the EMBEDDED menu instead of in the General Setup menu ? > + depends on X86_32 || PPC || PPC64 > + bool > + help > + Immediate values are used as read-mostly variables that are rarely > + updated. They use code patching to modify the values inscribed in the > + instruction stream. It provides a way to save precious cache lines > + that would otherwise have to be used by these variables. They can be > + disabled through the EMBEDDED menu. > + > menuconfig EMBEDDED > bool "Configure standard kernel features (for small systems)" > help > @@ -646,6 +657,16 @@ config PROC_KPAGEMAP > information on page-level memory usage. Disabling this interface > will reduce the size of the kernel by around 600 bytes. > > +config DISABLE_IMMEDIATE > + default y if EMBEDDED > + bool "Disable immediate values" if EMBEDDED > + depends on X86_32 || PPC || PPC64 > + help > + Disable code patching based immediate values for embedded systems. It > + consumes slightly more memory and requires to modify the instruction > + stream each time a variable is updated. Should really be disabled for > + embedded systems with read-only text. > + > endmenu # General setup > > config RT_MUTEXES --- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code ***