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trace: profile all if conditionals

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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>
This commit is contained in:
Steven Rostedt 2008-11-21 01:30:54 -05:00 • committed by Ingo Molnar
parent bac28bfe42
commit 2bcd521a68
4 changed files with 93 additions and 5 deletions
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38
include/linux/compiler.h
View file

@ -63,8 +63,16 @@ struct ftrace_branch_data {
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 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
# 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)