Be better about timeout rounding

src/core/iomgr/pollset_multipoller_with_epoll.c

@@ -100,8 +100,9 @@ static int multipoll_with_epoll_pollset_maybe_work(
   if (gpr_time_cmp(deadline, gpr_inf_future) == 0) {
     timeout_ms = -1;
   } else {
-    timeout_ms = gpr_time_to_millis(gpr_time_sub(deadline, now));
-    if (timeout_ms <= 0) {
+    timeout_ms = gpr_time_to_millis(
+        gpr_time_add(gpr_time_sub(deadline, now), gpr_time_from_micros(500)));
+    if (timeout_ms < 0) {
       return 1;
     }
   }

src/core/iomgr/pollset_multipoller_with_poll_posix.c

@@ -116,8 +116,9 @@ static int multipoll_with_poll_pollset_maybe_work(
   if (gpr_time_cmp(deadline, gpr_inf_future) == 0) {
     timeout = -1;
   } else {
-    timeout = gpr_time_to_millis(gpr_time_sub(deadline, now));
-    if (timeout <= 0) {
+    timeout = gpr_time_to_millis(
+        gpr_time_add(gpr_time_sub(deadline, now), gpr_time_from_micros(500)));
+    if (timeout < 0) {
       return 1;
     }
   }

src/core/iomgr/pollset_posix.c

@@ -346,8 +346,9 @@ static int basic_pollset_maybe_work(grpc_pollset *pollset,
   if (gpr_time_cmp(deadline, gpr_inf_future) == 0) {
     timeout = -1;
   } else {
-    timeout = gpr_time_to_millis(gpr_time_sub(deadline, now));
-    if (timeout <= 0) {
+    timeout = gpr_time_to_millis(
+        gpr_time_add(gpr_time_sub(deadline, now), gpr_time_from_micros(500)));
+    if (timeout < 0) {
       return 1;
     }
   }