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: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4e726b9..7742798 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -454,7 +454,10 @@
do { \
static const char *trace_printk_fmt \
__attribute__((section("__trace_printk_fmt"))); \
- trace_printk_fmt = 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 @@
do { \
static const char *trace_printk_fmt \
__attribute__((section("__trace_printk_fmt"))); \
- trace_printk_fmt = fmt; \
+ \
+ if (!trace_printk_fmt) \
+ trace_printk_fmt = fmt; \
+ \
__ftrace_vprintk(_THIS_IP_, trace_printk_fmt, vargs); \
} while (0)