MINOR: activity: report the number of times poll() reports I/O

The "show activity" output mentions a number of indicators to explain
wake up reasons but doesn't have the number of times poll() sees some
I/O. And given that multiple events can happen simultaneously, it's
not always possible to deduce this metric by subtracting.

This patch adds a new "poll_io" counter that allows one to see how
often poll() returns with at least one active FD. This should help
detect stuck events and measure various ratios of poll sub-metrics.

include/haproxy/activity-t.h

@@ -40,6 +40,7 @@ struct activity {
 	unsigned int loops;        // complete loops in run_poll_loop()
 	unsigned int wake_tasks;   // active tasks prevented poll() from sleeping
 	unsigned int wake_signal;  // pending signal prevented poll() from sleeping
+	unsigned int poll_io;      // number of times poll() reported I/O events
 	unsigned int poll_exp;     // number of times poll() sees an expired timeout (includes wake_*)
 	unsigned int poll_drop;    // poller dropped a dead FD from the update list
 	unsigned int poll_dead;    // poller woke up with a dead FD
@@ -51,7 +52,7 @@ struct activity {
 	unsigned int empty_rq;     // calls to process_runnable_tasks() with nothing for the thread
 	unsigned int long_rq;      // process_runnable_tasks() left with tasks in the run queue
 	unsigned int cpust_total;  // sum of half-ms stolen per thread
-	/* two unused entries left before end of first cache line */
+	/* one unused entry left before end of first cache line */
 	ALWAYS_ALIGN(64);
 
 	struct freq_ctr cpust_1s;  // avg amount of half-ms stolen over last second

src/cli.c

@@ -1129,6 +1129,7 @@ static int cli_io_handler_show_activity(struct appctx *appctx)
 	chunk_appendf(&trash, "loops:");        SHOW_TOT(thr, activity[thr].loops);
 	chunk_appendf(&trash, "wake_tasks:");   SHOW_TOT(thr, activity[thr].wake_tasks);
 	chunk_appendf(&trash, "wake_signal:");  SHOW_TOT(thr, activity[thr].wake_signal);
+	chunk_appendf(&trash, "poll_io:");      SHOW_TOT(thr, activity[thr].poll_io);
 	chunk_appendf(&trash, "poll_exp:");     SHOW_TOT(thr, activity[thr].poll_exp);
 	chunk_appendf(&trash, "poll_drop:");    SHOW_TOT(thr, activity[thr].poll_drop);
 	chunk_appendf(&trash, "poll_dead:");    SHOW_TOT(thr, activity[thr].poll_dead);

src/ev_epoll.c

@@ -180,8 +180,10 @@ static void _do_poll(struct poller *p, int exp, int wake)
 		status = epoll_wait(epoll_fd[tid], epoll_events, global.tune.maxpollevents, timeout);
 		tv_update_date(timeout, status);
 
-		if (status)
+		if (status) {
+			activity[tid].poll_io++;
 			break;
+		}
 		if (timeout || !wait_time)
 			break;
 		if (signal_queue_len || wake)

src/ev_evports.c

@@ -207,6 +207,9 @@ static void _do_poll(struct poller *p, int exp, int wake)
 
 	thread_harmless_end();
 
+	if (nevlist > 0)
+		activity[tid].poll_io++;
+
 	for (i = 0; i < nevlist; i++) {
 		unsigned int n = 0;
 		int events, rebind_events;

src/ev_kqueue.c

@@ -161,8 +161,10 @@ static void _do_poll(struct poller *p, int exp, int wake)
 		                &timeout_ts); // const struct timespec *timeout
 		tv_update_date(timeout, status);
 
-		if (status)
+		if (status) {
+			activity[tid].poll_io++;
 			break;
+		}
 		if (timeout || !wait_time)
 			break;
 		if (signal_queue_len || wake)

src/ev_poll.c

@@ -211,6 +211,9 @@ static void _do_poll(struct poller *p, int exp, int wake)
 
 	thread_harmless_end();
 
+	if (status > 0)
+		activity[tid].poll_io++;
+
 	for (count = 0; status > 0 && count < nbfd; count++) {
 		unsigned int n;
 		int e = poll_events[count].revents;

src/ev_select.c

@@ -188,6 +188,8 @@ static void _do_poll(struct poller *p, int exp, int wake)
 	if (status <= 0)
 		return;
 
+	activity[tid].poll_io++;
+
 	for (fds = 0; (fds * BITS_PER_INT) < maxfd; fds++) {
 		if ((((int *)(tmp_evts[DIR_RD]))[fds] | ((int *)(tmp_evts[DIR_WR]))[fds]) == 0)
 			continue;