[Tarantool-patches] [PATCH v2 1/2] fiber: reset clock stats on fiber.top_enable()

[Serge Petrenko <sergepetrenko@tarantool.org>]

We didn't refresh last remembered clock on fiber.top_enable()
This means that the fiber issuing fiber.top_enable() would get a huge
chunk of cpu time on its first yield. Fix this.
Also reset clock_delta and cpu_miss_count.

If fiber.top() is issued on the same ev loop iteration as
fiber.top_enable(), clock_delta_last is 0 for both cord and all the
fibers, so report "instant" and "average" stats per last iteration as 0
instead of NaN.

Follow-up #2694
---
 src/lib/core/fiber.c | 21 +++++++++++++++++++++
 src/lua/fiber.c      | 12 ++++++++++--
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
index aebaba7f0..258c094f5 100644
--- a/src/lib/core/fiber.c
+++ b/src/lib/core/fiber.c
@@ -1203,9 +1203,30 @@ fiber_top_enable()
 		ev_check_start(cord()->loop, &cord()->check_event);
 		fiber_top_enabled = true;
 
+		/*
+		 * Reset cord and fiber clock stats in order to
+		 * count from zero even on reenable.
+		 */
 		cord()->clock_acc = 0;
 		cord()->cpu_miss_count_last = 0;
 		cord()->clock_delta_last = 0;
+		cord()->clock_delta = 0;
+
+		struct fiber * fiber;
+		rlist_foreach_entry(fiber, &cord()->alive, link) {
+			fiber->clock_acc = 0;
+			fiber->clock_delta_last = 0;
+			fiber->clock_delta = 0;
+			fiber->cputime = 0;
+		}
+
+		cord()->sched.clock_acc = 0;
+		cord()->sched.clock_delta_last = 0;
+		cord()->sched.clock_delta = 0;
+		cord()->sched.cputime = 0;
+
+		cord()->clock_last = __rdtscp(&cord()->cpu_id_last);
+		cord()->cpu_miss_count = 0;
 		struct timespec ts;
 		if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
 			say_debug("clock_gettime(): failed to get this"
diff --git a/src/lua/fiber.c b/src/lua/fiber.c
index 8b3b22e55..647505643 100644
--- a/src/lua/fiber.c
+++ b/src/lua/fiber.c
@@ -335,11 +335,19 @@ lbox_fiber_top_entry(struct fiber *f, void *cb_ctx)
 	lua_newtable(L);
 
 	lua_pushliteral(L, "average");
-	lua_pushnumber(L, f->clock_acc / (double)cord()->clock_acc * 100);
+	if (cord()->clock_acc)
+		lua_pushnumber(L, f->clock_acc / (double)cord()->clock_acc * 100);
+	else
+		lua_pushnumber(L, 0);
 	lua_settable(L, -3);
+
 	lua_pushliteral(L, "instant");
-	lua_pushnumber(L, f->clock_delta_last / (double)cord()->clock_delta_last * 100);
+	if (cord()->clock_delta_last)
+		lua_pushnumber(L, f->clock_delta_last / (double)cord()->clock_delta_last * 100);
+	else
+		lua_pushnumber(L, 0);
 	lua_settable(L, -3);
+
 	lua_pushliteral(L, "time");
 	lua_pushnumber(L, f->cputime / (double) FIBER_TIME_RES);
 	lua_settable(L, -3);
-- 
2.21.0 (Apple Git-122)