From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bryan Wu Subject: Re: [gcv v3 18/35] drivers/leds: Replace __get_cpu_var uses Date: Tue, 3 Sep 2013 13:40:27 -0700 Message-ID: References: <20130828193457.140443630@linux.com> <00000140c67817ec-e0cb2a76-2b71-46e7-ba5f-0a3963bbd465-000000@email.amazonses.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Return-path: Received: from mail-lb0-f173.google.com ([209.85.217.173]:42401 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755932Ab3ICUkt (ORCPT ); Tue, 3 Sep 2013 16:40:49 -0400 In-Reply-To: <00000140c67817ec-e0cb2a76-2b71-46e7-ba5f-0a3963bbd465-000000@email.amazonses.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Christoph Lameter Cc: Tejun Heo , akpm@linuxfoundation.org, linux-arch@vger.kernel.org, Steven Rostedt , lkml On Wed, Aug 28, 2013 at 12:48 PM, 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. > > Other use 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 an 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 an 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. > > > > > 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(&x), y, 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/drivers/leds/trigger/ledtrig-cpu.c > =================================================================== > --- linux.orig/drivers/leds/trigger/ledtrig-cpu.c 2013-08-27 14:46:42.043176071 -0500 > +++ linux/drivers/leds/trigger/ledtrig-cpu.c 2013-08-27 14:46:42.035176153 -0500 > @@ -46,7 +46,7 @@ static DEFINE_PER_CPU(struct led_trigger > */ > void ledtrig_cpu(enum cpu_led_event ledevt) > { > - struct led_trigger_cpu *trig = &__get_cpu_var(cpu_trig); > + struct led_trigger_cpu *trig = this_cpu_ptr(&cpu_trig); > Sure, please go ahead with my ack. Acked-by: Bryan Wu > /* Locate the correct CPU LED */ > switch (ledevt) { >