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Date: Wed, 28 Aug 2013 15:48:04 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Christoph Lameter <cl@...ux.com>
Cc: Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>, linux-arch@...r.kernel.org,
Steven Rostedt <srostedt@...hat.com>,
linux-kernel@...r.kernel.org,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [guv v2 08/31] tracing: Replace __get_cpu_var uses
On Mon, 26 Aug 2013 20:44:37 +0000
Christoph Lameter <cl@...ux.com> 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 <cl@...ux.com>
>
> 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)
--
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