From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754460Ab3H1TsJ (ORCPT ); Wed, 28 Aug 2013 15:48:09 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:11007 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753078Ab3H1TsH (ORCPT ); Wed, 28 Aug 2013 15:48:07 -0400 X-Authority-Analysis: v=2.0 cv=ddwCLAre c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=xzSgfWsWOV0A:10 a=5SG0PmZfjMsA:10 a=kj9zAlcOel0A:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=LG-SUfS54wIA:10 a=NufY4J3AAAAA:8 a=5R1lbcN1xY39T-RM1zsA:9 a=CjuIK1q_8ugA:10 a=re9sYKne76oA:10 a=BmzZ8hBqutQhxNjl:21 a=Hwd3F8jQxMoHXz-7:21 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Date: Wed, 28 Aug 2013 15:48:04 -0400 From: Steven Rostedt To: Christoph Lameter Cc: Tejun Heo , akpm@linuxfoundation.org, Frederic Weisbecker , Ingo Molnar , linux-arch@vger.kernel.org, Steven Rostedt , linux-kernel@vger.kernel.org, Masami Hiramatsu Subject: Re: [guv v2 08/31] tracing: Replace __get_cpu_var uses Message-ID: <20130828154804.20f4dde6@gandalf.local.home> In-Reply-To: <00000140bc5f00c2-8e9ffffa-de46-4329-aef3-317c258828bd-000000@email.amazonses.com> References: <20130826204351.725357339@linux.com> <00000140bc5f00c2-8e9ffffa-de46-4329-aef3-317c258828bd-000000@email.amazonses.com> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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! -- Steve > > int register_kprobe(struct kprobe *p); > Index: linux/kernel/trace/ftrace.c > =================================================================== > --- linux.orig/kernel/trace/ftrace.c 2013-08-26 14:25:53.000000000 -0500 > +++ linux/kernel/trace/ftrace.c 2013-08-26 14:26:29.460993659 -0500 > @@ -870,7 +870,7 @@ function_profile_call(unsigned long ip, > > local_irq_save(flags); > > - stat = &__get_cpu_var(ftrace_profile_stats); > + stat = this_cpu_ptr(&ftrace_profile_stats); > if (!stat->hash || !ftrace_profile_enabled) > goto out; > > @@ -901,7 +901,7 @@ static void profile_graph_return(struct > unsigned long flags; > > local_irq_save(flags); > - stat = &__get_cpu_var(ftrace_profile_stats); > + stat = this_cpu_ptr(&ftrace_profile_stats); > if (!stat->hash || !ftrace_profile_enabled) > goto out; > > Index: linux/kernel/trace/trace.c > =================================================================== > --- linux.orig/kernel/trace/trace.c 2013-08-26 14:25:53.000000000 -0500 > +++ linux/kernel/trace/trace.c 2013-08-26 14:26:29.464993617 -0500 > @@ -1676,7 +1676,7 @@ static void __ftrace_trace_stack(struct > */ > barrier(); > if (use_stack == 1) { > - trace.entries = &__get_cpu_var(ftrace_stack).calls[0]; > + trace.entries = this_cpu_ptr(ftrace_stack.calls); > trace.max_entries = FTRACE_STACK_MAX_ENTRIES; > > if (regs)