backend-drm: Count and display KMS page flips

This patch counts the page flips (either in atomic or legacy page flips)
for DRM outputs and prints them using the drm-backend scope.

Similar to the frame callback timer counter this installs a counter that
periodically computes page flips per a pre-defined interval.

This also includes a perfetto counter to display these in perfetto.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

libweston/backend-drm/drm-internal.h

@@ -272,6 +272,11 @@ struct drm_backend {
 	bool has_underlay;
 
 	struct weston_log_scope *debug;
+
+	struct {
+		uint32_t frame_counter_interval;
+		struct wl_event_source *pageflip_timer_counter;
+	} perf_page_flips_stats;
 };
 
 struct drm_mode {
@@ -601,6 +606,12 @@ struct drm_output {
 
 	struct wl_event_source *pageflip_timer;
 
+	/* how many page flips */
+	uint32_t page_flips_counted;
+
+	/* how many page flips / interval */
+	float page_flips_per_timer_interval;
+
 	bool is_virtual;
 	void (*virtual_destroy)(struct weston_output *base);
 

libweston/backend-drm/drm.c

@@ -58,6 +58,7 @@
 #include "shared/string-helpers.h"
 #include "shared/weston-drm-fourcc.h"
 #include "output-capture.h"
+#include "weston-trace.h"
 #include "pixman-renderer.h"
 #include "pixel-formats.h"
 #include "libbacklight.h"
@@ -189,6 +190,64 @@ drm_output_pageflip_timer_create(struct drm_output *output)
 	return 0;
 }
 
+static int
+pageflip_timer_counter_handler(void *data)
+{
+	struct drm_backend *b = data;
+	struct weston_compositor *ec = b->compositor;
+	struct weston_output *output_base;
+
+	wl_list_for_each(output_base, &ec->output_list, link) {
+		struct drm_output *output = to_drm_output(output_base);
+		char desc[1024];
+
+		output->page_flips_per_timer_interval =
+			(float) (output->page_flips_counted /
+					b->perf_page_flips_stats.frame_counter_interval);
+
+		snprintf(desc, sizeof(desc),
+			 "output %s KMS page flips", output_base->name);
+
+		WESTON_TRACE_SET_COUNTER(desc,
+					output->page_flips_per_timer_interval);
+
+		output->page_flips_counted = 0;
+	}
+
+
+	wl_event_source_timer_update(b->perf_page_flips_stats.pageflip_timer_counter,
+				     1000 * b->perf_page_flips_stats.frame_counter_interval);
+
+	return 0;
+}
+
+static int
+drm_backend_pageflip_timer_create(struct drm_backend *b, uint32_t interval)
+{
+	struct wl_event_loop *loop = NULL;
+	struct weston_compositor *ec = b->compositor;
+
+	loop = wl_display_get_event_loop(ec->wl_display);
+	assert(loop);
+
+	b->perf_page_flips_stats.pageflip_timer_counter =
+		wl_event_loop_add_timer(loop, pageflip_timer_counter_handler, b);
+
+	if (b->perf_page_flips_stats.pageflip_timer_counter == NULL) {
+		weston_log("creating drm pageflip counter timer failed: %s\n",
+			   strerror(errno));
+		return -1;
+	}
+
+	b->perf_page_flips_stats.frame_counter_interval = interval;
+
+	/* arm it w/ interval */
+	wl_event_source_timer_update(b->perf_page_flips_stats.pageflip_timer_counter,
+				     1000 * b->perf_page_flips_stats.frame_counter_interval);
+
+	return 0;
+}
+
 /**
  * Returns true if the plane can be used on the given output for its current
  * repaint cycle.
@@ -3478,6 +3537,7 @@ drm_shutdown(struct weston_backend *backend)
 
 	wl_event_source_remove(b->udev_drm_source);
 	wl_event_source_remove(b->drm_source);
+	wl_event_source_remove(b->perf_page_flips_stats.pageflip_timer_counter);
 
 	/* We are shutting down. This function destroy the planes with
 	 * destroy_sprites() and then calls weston_compositor_shutdown(), which
@@ -4267,6 +4327,8 @@ drm_backend_create(struct weston_compositor *compositor,
 		goto err_udev_monitor;
 	}
 
+	drm_backend_pageflip_timer_create(b, DEFAULT_FRAME_RATE_INTERVAL);
+
 	return b;
 
 err_udev_monitor:

libweston/backend-drm/kms.c

@@ -1884,6 +1884,7 @@ page_flip_handler(int fd, unsigned int frame,
 	assert(output->page_flip_pending);
 	output->page_flip_pending = false;
 
+	output->page_flips_counted++;
 	drm_output_update_complete(output, flags, sec, usec);
 }
 
@@ -1905,6 +1906,7 @@ atomic_flip_handler(int fd, unsigned int frame, unsigned int sec,
 	assert(crtc);
 
 	output = crtc->output;
+	output->page_flips_counted++;
 
 	/* During the initial modeset, we can disable CRTCs which we don't
 	 * actually handle during normal operation; this will give us events
@@ -1932,6 +1934,9 @@ atomic_flip_handler(int fd, unsigned int frame, unsigned int sec,
 
 	drm_output_update_complete(output, flags, sec, usec);
 	drm_debug(b, "[atomic][CRTC:%u] flip processing completed\n", crtc_id);
+	drm_debug(b, "[atomic][CRTC:%u] %.2f page flips computed in %d seconds\n",
+			crtc_id, output->page_flips_per_timer_interval,
+			output->backend->perf_page_flips_stats.frame_counter_interval);
 }
 
 int

libweston/compositor.c

@@ -98,7 +98,6 @@
  */
 
 #define DEFAULT_REPAINT_WINDOW 7 /* milliseconds */
-#define DEFAULT_FRAME_RATE_INTERVAL 1 /* seconds */
 
 static void
 weston_output_transform_scale_init(struct weston_output *output,

libweston/libweston-internal.h

@@ -44,6 +44,8 @@
 #include <assert.h>
 #include "color.h"
 
+#define DEFAULT_FRAME_RATE_INTERVAL 1 /* seconds */
+
 /* compositor <-> renderer interface */
 
 /** Opaque pointer to renderbuffer data.