Re: [tip:tracing/printk] tracing: optimize trace_printk()
- From: Steven Rostedt <rostedt@xxxxxxxxxxx>
- Date: Mon, 9 Mar 2009 13:23:12 -0400 (EDT)
On Mon, 9 Mar 2009, Ingo Molnar wrote:
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@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
LKML-Reference: <1236356510-8381-5-git-send-email-fweisbec@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
include/linux/kernel.h | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
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 { \
do { \
static const char *trace_printk_fmt \
__attribute__((section("__trace_printk_fmt"))); \
- trace_printk_fmt = fmt; \
+ \
+ if (!trace_printk_fmt) \
+ trace_printk_fmt = fmt; \
+ \
But this is a static init. That is, it is done at initialization and not
every time.
The change actually slows down the system.
__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"))); \
- trace_printk_fmt = fmt; \
+ \
+ if (!trace_printk_fmt) \
+ trace_printk_fmt = fmt; \
+ \
Same here.
-- Steve
__ftrace_vprintk(_THIS_IP_, trace_printk_fmt, vargs); \--
} while (0)
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- References:
- [PATCH 4/5 v3] tracing/core: drop the old ftrace_printk implementation in favour of ftrace_bprintk
- From: Frederic Weisbecker
- [tip:tracing/printk] tracing: optimize trace_printk()
- From: Ingo Molnar
- [PATCH 4/5 v3] tracing/core: drop the old ftrace_printk implementation in favour of ftrace_bprintk
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