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Commit 7bffc23e authored by Ingo Molnar's avatar Ingo Molnar
Browse files

tracing: optimize trace_printk() 



Impact: micro-optimization

trace_printk() does this unconditionally:

	trace_printk_fmt = fmt;

Where trace_printk_fmt is an entry into a global array. This is
very SMP-unfriendly.

So only write it once per bootup.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1236356510-8381-5-git-send-email-fweisbec@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8a20d84d

include/linux/kernel.h

+8 −2
Original line number Diff line number Diff line
@@ -454,7 +454,10 @@ do { \ 
do {									\

	static const char *trace_printk_fmt				\

	__attribute__((section("__trace_printk_fmt")));			\

									\

	if (!trace_printk_fmt)						\

		trace_printk_fmt = fmt;					\

									\

	__trace_printk_check_format(fmt, ##args);			\

	__trace_printk(_THIS_IP_, trace_printk_fmt, ##args);		\

} while (0)
@@ -467,7 +470,10 @@ __trace_printk(unsigned long ip, const char *fmt, ...) 
do {									\

	static const char *trace_printk_fmt				\

	__attribute__((section("__trace_printk_fmt")));			\

									\

	if (!trace_printk_fmt)						\

		trace_printk_fmt = fmt;					\

									\

	__ftrace_vprintk(_THIS_IP_, trace_printk_fmt, vargs);		\

} while (0)