[igt-dev] [PATCH i-g-t] intel_gpu_top: Use actual period when calculating client busyness

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

On a slow machine, or with many processes and/or file descriptors to
parse, the period of the scanning loop can drift significantly from the
assumed value. This results in artificially inflated client busyness
percentages.

To alleviate the issue take some real timestamps and use actual elapsed
time when calculating relative busyness.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 tools/intel_gpu_top.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/tools/intel_gpu_top.c b/tools/intel_gpu_top.c
index e13e35b71f4b..af4b350da8e4 100644
--- a/tools/intel_gpu_top.c
+++ b/tools/intel_gpu_top.c
@@ -43,6 +43,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 #include <termios.h>
+#include <time.h>
 #include <sys/sysmacros.h>
 
 #include "igt_perf.h"
@@ -2524,6 +2525,38 @@ static void show_help_screen(void)
 "\n");
 }
 
+static int gettime(struct timespec *ts)
+{
+	memset(ts, 0, sizeof(*ts));
+
+#ifdef CLOCK_MONOTONIC_RAW
+	if (!clock_gettime(CLOCK_MONOTONIC_RAW, ts))
+		return 0;
+#endif
+#ifdef CLOCK_MONOTONIC_COARSE
+	if (!clock_gettime(CLOCK_MONOTONIC_COARSE, ts))
+		return 0;
+#endif
+
+	return clock_gettime(CLOCK_MONOTONIC, ts);
+}
+
+static unsigned long elapsed_us(struct timespec *prev, unsigned int period_us)
+{
+	unsigned long elapsed;
+	struct timespec now;
+
+	if (gettime(&now))
+		return period_us;
+
+	elapsed = ((now.tv_nsec - prev->tv_nsec) / 1000 +
+	           (unsigned long)USEC_PER_SEC * (now.tv_sec - prev->tv_sec));
+
+	*prev = now;
+
+	return elapsed;
+}
+
 int main(int argc, char **argv)
 {
 	unsigned int period_us = DEFAULT_PERIOD_MS * 1000;
@@ -2537,6 +2570,7 @@ int main(int argc, char **argv)
 	char *pmu_device, *opt_device = NULL;
 	struct igt_device_card card;
 	char *codename = NULL;
+	struct timespec ts;
 
 	/* Parse options */
 	while ((ch = getopt(argc, argv, "o:s:d:pcJLlh")) != -1) {
@@ -2690,6 +2724,7 @@ int main(int argc, char **argv)
 
 	pmu_sample(engines);
 	scan_clients(clients, false);
+	gettime(&ts);
 	codename = igt_device_get_pretty_name(&card, false);
 
 	if (output_mode == JSON)
@@ -2698,6 +2733,7 @@ int main(int argc, char **argv)
 	while (!stop_top) {
 		struct clients *disp_clients;
 		bool consumed = false;
+		unsigned int scan_us;
 		int j, lines = 0;
 		struct winsize ws;
 		struct client *c;
@@ -2720,6 +2756,7 @@ int main(int argc, char **argv)
 		t = (double)(engines->ts.cur - engines->ts.prev) / 1e9;
 
 		disp_clients = scan_clients(clients, true);
+		scan_us = elapsed_us(&ts, period_us);
 
 		if (stop_top)
 			break;
@@ -2757,7 +2794,7 @@ int main(int argc, char **argv)
 
 					lines = print_client(c, engines, t,
 							     lines, con_w,
-							     con_h, period_us,
+							     con_h, scan_us,
 							     &class_w);
 				}
 
-- 
2.37.2