linux-kernel - [tip:perf/core] tracing: Use __this_cpu_inc/ dec operation instead of __get_cpu

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Message-ID: <tip-821465295b36136998ef294fe176fba4e09c1cd9@git.kernel.org>
Date:	Sun, 3 Feb 2013 11:18:05 -0800
From:	tip-bot for Shan Wei <davidshan@...cent.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	davidshan@...cent.com, rostedt@...dmis.org, cl@...ux.com,
	tglx@...utronix.de
Subject: [tip:perf/core] tracing: Use __this_cpu_inc/
 dec operation instead of __get_cpu_var

Commit-ID:  821465295b36136998ef294fe176fba4e09c1cd9
Gitweb:     http://git.kernel.org/tip/821465295b36136998ef294fe176fba4e09c1cd9
Author:     Shan Wei <davidshan@...cent.com>
AuthorDate: Mon, 19 Nov 2012 13:21:01 +0800
Committer:  Steven Rostedt <rostedt@...dmis.org>
CommitDate: Fri, 25 Jan 2013 20:36:54 -0500

tracing: Use __this_cpu_inc/dec operation instead of __get_cpu_var

__this_cpu_inc_return() or __this_cpu_dec generates a single instruction,
which is faster than __get_cpu_var operation.

Link: http://lkml.kernel.org/r/50A9C1BD.1060308@gmail.com

Reviewed-by: Christoph Lameter <cl@...ux.com>
Signed-off-by: Shan Wei <davidshan@...cent.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/trace.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ca9b7df..07888e1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1344,7 +1344,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
 	 */
 	preempt_disable_notrace();
 
-	use_stack = ++__get_cpu_var(ftrace_stack_reserve);
+	use_stack = __this_cpu_inc_return(ftrace_stack_reserve);
 	/*
 	 * We don't need any atomic variables, just a barrier.
 	 * If an interrupt comes in, we don't care, because it would
@@ -1398,7 +1398,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
  out:
 	/* Again, don't let gcc optimize things here */
 	barrier();
-	__get_cpu_var(ftrace_stack_reserve)--;
+	__this_cpu_dec(ftrace_stack_reserve);
 	preempt_enable_notrace();
 
 }
--
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