trace: profile all if conditionals
Impact: feature to profile if statements
This patch adds a branch profiler for all if () statements.
The results will be found in:
/debugfs/tracing/profile_branch
For example:
miss hit % Function File Line
------- --------- - -------- ---- ----
0 1 100 x86_64_start_reservations head64.c 127
0 1 100 copy_bootdata head64.c 69
1 0 0 x86_64_start_kernel head64.c 111
32 0 0 set_intr_gate desc.h 319
1 0 0 reserve_ebda_region head.c 51
1 0 0 reserve_ebda_region head.c 47
0 1 100 reserve_ebda_region head.c 42
0 0 X maxcpus main.c 165
Miss means the branch was not taken. Hit means the branch was taken.
The percent is the percentage the branch was taken.
This adds a significant amount of overhead and should only be used
by those analyzing their system.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 0628a20..ea7c6be 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -63,8 +63,16 @@
const char *func;
const char *file;
unsigned line;
- unsigned long correct;
- unsigned long incorrect;
+ union {
+ struct {
+ unsigned long correct;
+ unsigned long incorrect;
+ };
+ struct {
+ unsigned long miss;
+ unsigned long hit;
+ };
+ };
};
/*
@@ -103,6 +111,32 @@
# ifndef unlikely
# define unlikely(x) (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 0))
# endif
+
+#ifdef CONFIG_PROFILE_ALL_BRANCHES
+/*
+ * "Define 'is'", Bill Clinton
+ * "Define 'if'", Steven Rostedt
+ */
+#define if(cond) if (__builtin_constant_p((cond)) ? !!(cond) : \
+ ({ \
+ int ______r; \
+ static struct ftrace_branch_data \
+ __attribute__((__aligned__(4))) \
+ __attribute__((section("_ftrace_branch"))) \
+ ______f = { \
+ .func = __func__, \
+ .file = __FILE__, \
+ .line = __LINE__, \
+ }; \
+ ______r = !!(cond); \
+ if (______r) \
+ ______f.hit++; \
+ else \
+ ______f.miss++; \
+ ______r; \
+ }))
+#endif /* CONFIG_PROFILE_ALL_BRANCHES */
+
#else
# define likely(x) __builtin_expect(!!(x), 1)
# define unlikely(x) __builtin_expect(!!(x), 0)