tracing: optimize trace_printk() (7bffc23e) · Commits · 戴 / test

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:

Ingo Molnar <mingo@elte.hu>

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)

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