From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755513Ab3H2DoI (ORCPT ); Wed, 28 Aug 2013 23:44:08 -0400 Received: from mail7.hitachi.co.jp ([133.145.228.42]:46124 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755277Ab3H2DoG (ORCPT ); Wed, 28 Aug 2013 23:44:06 -0400 Message-ID: <521EC382.5070406@hitachi.com> Date: Thu, 29 Aug 2013 12:44:02 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Steven Rostedt Cc: Christoph Lameter , Tejun Heo , akpm@linuxfoundation.org, Frederic Weisbecker , Ingo Molnar , linux-arch@vger.kernel.org, Steven Rostedt , linux-kernel@vger.kernel.org Subject: Re: [guv v2 08/31] tracing: Replace __get_cpu_var uses References: <20130826204351.725357339@linux.com> <00000140bc5f00c2-8e9ffffa-de46-4329-aef3-317c258828bd-000000@email.amazonses.com> <20130828154804.20f4dde6@gandalf.local.home> In-Reply-To: <20130828154804.20f4dde6@gandalf.local.home> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2013/08/29 4:48), Steven Rostedt wrote: > On Mon, 26 Aug 2013 20:44:37 +0000 > Christoph Lameter wrote: > >> __get_cpu_var() is used for multiple purposes in the kernel source. One of them is >> address calculation via the form &__get_cpu_var(x). This calculates the address for >> the instance of the percpu variable of the current processor based on an offset. >> >> Others usage cases are for storing and retrieving data from the current processors percpu area. >> __get_cpu_var() can be used as an lvalue when writing data or on the right side of an assignment. >> >> __get_cpu_var() is defined as : >> >> >> #define __get_cpu_var(var) (*this_cpu_ptr(&(var))) >> >> >> >> __get_cpu_var() always only does a address determination. However, store and retrieve operations >> could use a segment prefix (or global register on other platforms) to avoid the address calculation. >> >> this_cpu_write() and this_cpu_read() can directly take an offset into a percpu area and use >> optimized assembly code to read and write per cpu variables. >> >> >> This patch converts __get_cpu_var into either and explicit address calculation using this_cpu_ptr() >> or into a use of this_cpu operations that use the offset. Thereby address calcualtions are avoided >> and less registers are used when code is generated. >> >> At the end of the patchset all uses of __get_cpu_var have been removed so the macro is removed too. >> >> The patchset includes passes over all arches as well. Once these operations are used throughout then >> specialized macros can be defined in non -x86 arches as well in order to optimize per cpu access by >> f.e. using a global register that may be set to the per cpu base. > > You should limit the width of the change log to 76 characters. > > I fixed it for now. > >> >> >> >> >> Transformations done to __get_cpu_var() >> >> >> 1. Determine the address of the percpu instance of the current processor. >> >> DEFINE_PER_CPU(int, y); >> int *x = &__get_cpu_var(y); >> >> Converts to >> >> int *x = this_cpu_ptr(&y); >> >> >> 2. Same as #1 but this time an array structure is involved. >> >> DEFINE_PER_CPU(int, y[20]); >> int *x = __get_cpu_var(y); >> >> Converts to >> >> int *x = this_cpu_ptr(y); >> >> >> 3. Retrieve the content of the current processors instance of a per cpu variable. >> >> DEFINE_PER_CPU(int, u); >> int x = __get_cpu_var(y) >> >> Converts to >> >> int x = __this_cpu_read(y); >> >> >> 4. Retrieve the content of a percpu struct >> >> DEFINE_PER_CPU(struct mystruct, y); >> struct mystruct x = __get_cpu_var(y); >> >> Converts to >> >> memcpy(this_cpu_ptr(&y), x, sizeof(x)); >> >> >> 5. Assignment to a per cpu variable >> >> DEFINE_PER_CPU(int, y) >> __get_cpu_var(y) = x; >> >> Converts to >> >> this_cpu_write(y, x); >> >> >> 6. Increment/Decrement etc of a per cpu variable >> >> DEFINE_PER_CPU(int, y); >> __get_cpu_var(y)++ >> >> Converts to >> >> this_cpu_inc(y) >> >> >> Signed-off-by: Christoph Lameter >> >> Index: linux/include/linux/kprobes.h >> =================================================================== >> --- linux.orig/include/linux/kprobes.h 2013-08-26 14:25:53.000000000 -0500 >> +++ linux/include/linux/kprobes.h 2013-08-26 14:26:29.460993659 -0500 >> @@ -329,7 +329,7 @@ static inline void reset_current_kprobe( >> >> static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void) >> { >> - return (&__get_cpu_var(kprobe_ctlblk)); >> + return this_cpu_ptr(&kprobe_ctlblk); >> } > > Masami, > > Can you give me an Acked-by: for this. > Thanks for pinging me ;) Acked-by: Masami Hiramatsu Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com