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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@tencent.com>
AuthorDate: Mon, 19 Nov 2012 13:21:01 +0800
Committer: Steven Rostedt <rostedt@goodmis.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@linux.com>
Signed-off-by: Shan Wei <davidshan@tencent.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.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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