[PATCH 2/3] perf debug: Avoid calling eprintf() in pr_debugN() when verbose < n

[Ian Rogers <irogers@google.com>]

pr_debugN() unconditionally evaluated its arguments and called eprintf() ->
veprintf() before checking if verbose >= n. In hot paths such as
dso__load_sym_internal(), two pr_debug4() calls per symbol accounted for
~15% of total CPU time in 'perf top' even at the default verbose == 0.

Guard eprintf() in pr_debugN() with unlikely(verbose >= (n)) and define
pr_debug() in terms of pr_debugN(1, ...).

In test__parsing_callback() (tools/perf/tests/pmu-events.c), move the
test_generic_metric(mexp, 0) call out of the pr_debug() argument list so
the metric evaluation continues to run during 'perf test' when verbose == 0.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/tests/pmu-events.c | 5 ++++-
 tools/perf/util/debug.h       | 5 ++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/perf/tests/pmu-events.c b/tools/perf/tests/pmu-events.c
index f507ce39439a..e6e4f4cf1fa2 100644
--- a/tools/perf/tests/pmu-events.c
+++ b/tools/perf/tests/pmu-events.c
@@ -906,9 +906,12 @@ static int test__parsing_callback(const struct pmu_metric *pm,
 			struct metric_expr *mexp;
 
 			list_for_each_entry (mexp, &me->head, nd) {
+				double result;
+
 				if (strcmp(mexp->metric_name, pm->metric_name))
 					continue;
-				pr_debug("Result %f\n", test_generic_metric(mexp, 0));
+				result = test_generic_metric(mexp, 0);
+				pr_debug("Result %f\n", result);
 				err = 0;
 				(*failures)--;
 				goto out_err;
diff --git a/tools/perf/util/debug.h b/tools/perf/util/debug.h
index 6b737e195ce1..7552c9171d90 100644
--- a/tools/perf/util/debug.h
+++ b/tools/perf/util/debug.h
@@ -33,10 +33,9 @@ extern int debug_type_profile;
 })
 #define pr_info(fmt, ...) \
 	eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
-#define pr_debug(fmt, ...) \
-	eprintf(1, verbose, pr_fmt(fmt), ##__VA_ARGS__)
 #define pr_debugN(n, fmt, ...) \
-	eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__)
+	(unlikely(verbose >= (n)) ? eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__) : 0)
+#define pr_debug(fmt, ...) pr_debugN(1, pr_fmt(fmt), ##__VA_ARGS__)
 #define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
 #define pr_debug3(fmt, ...) pr_debugN(3, pr_fmt(fmt), ##__VA_ARGS__)
 #define pr_debug4(fmt, ...) pr_debugN(4, pr_fmt(fmt), ##__VA_ARGS__)
-- 
2.56.0.307.g5fe7bd680c-goog