tracing: optimization of branch tracer

Impact: better performance for if branch tracer

Use an array to count the hit and misses of a conditional instead
of using another conditional. This cuts down on saturation of branch
predictions and increases performance of modern pipelined architectures.

Signed-off-by: Witold Baryluk <baryluk@smp.if.uj.edu.pl>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index d95da10..6faa7e5 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -68,6 +68,7 @@ struct ftrace_branch_data {
                        unsigned long miss;
                        unsigned long hit;
                };
+               unsigned long miss_hit[2];
        };
 };
 
@@ -125,10 +126,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
                                .line = __LINE__,                       \
                        };                                              \
                ______r = !!(cond);                                     \
-               if (______r)                                            \
-                       ______f.hit++;                                  \
-               else                                                    \
-                       ______f.miss++;                                 \
+               ______f.miss_hit[______r]++;                                    \
                ______r;                                                \
        }))
 #endif /* CONFIG_PROFILE_ALL_BRANCHES */