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>

1 files changed, 16 insertions, 0 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 7e3548705708..61e8cca6ff45 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -173,6 +173,22 @@ config TRACE_BRANCH_PROFILING
 
           Say N if unsure.
 
+config PROFILE_ALL_BRANCHES
+        bool "Profile all if conditionals"
+        depends on TRACE_BRANCH_PROFILING
+        help
+          This tracer profiles all branch conditions. Every if ()
+          taken in the kernel is recorded whether it hit or miss.
+          The results will be displayed in:
+
+          /debugfs/tracing/profile_branch
+
+          This configuration, when enabled, will impose a great overhead
+          on the system. This should only be enabled when the system
+          is to be analyzed
+
+          Say N if unsure.
+
 config TRACING_BRANCHES
         bool
         help