Add kernel tracing instrumentation

alloc.c

@@ -7,6 +7,7 @@
 #include <unistd.h>
 #include "log.h"
 #include "private.h"
+#include "trace.h"
 
 /* Plane allocation algorithm
  *
@@ -674,6 +675,10 @@ liftoff_output_apply(struct liftoff_output *output, drmModeAtomicReq *req,
 
 	update_layers_priority(device);
 
+	liftoff_tracer_mark(&device->tracer,
+			    "output_apply (begin_ctx=%d)",
+			    device->page_flip_counter);
+
 	ret = reuse_previous_alloc(output, req, flags);
 	if (ret == 0) {
 		log_reuse(output);
@@ -776,5 +781,9 @@ liftoff_output_apply(struct liftoff_output *output, drmModeAtomicReq *req,
 
 	mark_layers_clean(output);
 
+	liftoff_tracer_mark(&device->tracer,
+			    "output_apply (end_ctx=%d)",
+			    device->page_flip_counter);
+
 	return 0;
 }

device.c

@@ -20,6 +20,8 @@ liftoff_device_create(int drm_fd)
 	liftoff_list_init(&device->planes);
 	liftoff_list_init(&device->outputs);
 
+	liftoff_tracer_init(&device->tracer);
+
 	device->drm_fd = dup(drm_fd);
 	if (device->drm_fd < 0) {
 		liftoff_log_errno(LIFTOFF_ERROR, "dup");
@@ -59,6 +61,7 @@ liftoff_device_destroy(struct liftoff_device *device)
 		return;
 	}
 
+	liftoff_tracer_finish(&device->tracer);
 	close(device->drm_fd);
 	liftoff_list_for_each_safe(plane, tmp, &device->planes, link) {
 		liftoff_plane_destroy(plane);
@@ -97,6 +100,10 @@ device_test_commit(struct liftoff_device *device, drmModeAtomicReq *req,
 
 	device->test_commit_counter++;
 
+	liftoff_tracer_mark(&device->tracer,
+			    "device_test_commit (begin_ctx=%d)",
+			    device->test_commit_counter);
+
 	flags &= ~DRM_MODE_PAGE_FLIP_EVENT;
 	do {
 		ret = drmModeAtomicCommit(device->drm_fd, req,
@@ -104,6 +111,10 @@ device_test_commit(struct liftoff_device *device, drmModeAtomicReq *req,
 					  NULL);
 	} while (ret == -EINTR || ret == -EAGAIN);
 
+	liftoff_tracer_mark(&device->tracer,
+			    "device_test_commit (end_ctx=%d)",
+			    device->test_commit_counter);
+
 	/* The kernel will return -EINVAL for invalid configuration, -ERANGE for
 	 * CRTC coords overflow, and -ENOSPC for invalid SRC coords. */
 	if (ret != 0 && ret != -EINVAL && ret != -ERANGE && ret != -ENOSPC) {

include/private.h

@@ -4,6 +4,7 @@
 #include <libliftoff.h>
 #include "list.h"
 #include "log.h"
+#include "trace.h"
 
 /* Layer priority is assigned depending on the number of updates during a
  * given number of page-flips */
@@ -18,6 +19,7 @@ struct liftoff_device {
 	uint32_t *crtcs;
 	size_t crtcs_len;
 
+	struct liftoff_tracer tracer;
 	int page_flip_counter;
 	int test_commit_counter;
 };

include/trace.h

@@ -0,0 +1,21 @@
+#ifndef TRACE_H
+#define TRACE_H
+
+#include <stdio.h>
+#include "log.h"
+
+struct liftoff_tracer {
+	FILE *f;
+};
+
+int
+liftoff_tracer_init(struct liftoff_tracer *tracer);
+
+void
+liftoff_tracer_finish(struct liftoff_tracer *tracer);
+
+void
+liftoff_tracer_mark(struct liftoff_tracer *tracer, const char *format, ...)
+_LIFTOFF_ATTRIB_PRINTF(2, 3);
+
+#endif

meson.build

@@ -38,6 +38,7 @@ liftoff_lib = library(
 		'log.c',
 		'output.c',
 		'plane.c',
+		'trace.c',
 	),
 	include_directories: liftoff_inc,
 	version: meson.project_version(),

trace.c

@@ -0,0 +1,39 @@
+#include <errno.h>
+#include "trace.h"
+
+int
+liftoff_tracer_init(struct liftoff_tracer *tracer)
+{
+	tracer->f = fopen("/sys/kernel/tracing/trace_marker", "w");
+	if (tracer->f == NULL) {
+		return -errno;
+	}
+	liftoff_log(LIFTOFF_DEBUG, "Kernel tracing is enabled");
+	return 0;
+}
+
+void
+liftoff_tracer_finish(struct liftoff_tracer *tracer)
+{
+	if (tracer->f != NULL) {
+		fclose(tracer->f);
+	}
+}
+
+void
+liftoff_tracer_mark(struct liftoff_tracer *tracer, const char *format, ...)
+{
+	if (tracer->f == NULL) {
+		return;
+	}
+
+	fprintf(tracer->f, "libliftoff: ");
+
+	va_list args;
+	va_start(args, format);
+	vfprintf(tracer->f, format, args);
+	va_end(args);
+
+	fprintf(tracer->f, "\n");
+	fflush(tracer->f);
+}