Do something sensible for timestamp wrapping.

[fips] / metrics.c

diff --git a/metrics.c b/metrics.c
index e37618665d508cf67bd9614bae65665f229bccd0..c52bf2ee6c3557dd6b8b41dda820ac24bced4e5b 100644 (file)
--- a/metrics.c
+++ b/metrics.c
@@ -113,6 +113,28 @@ struct metrics
        struct timespec cpu_time_ts;
 };
 
+/* Return (a - b) while accounting for the fact that between a and b,
+ * the counter may have wrapped around (with a maximum number of bits
+ * in the counter of GL_QUERY_COUNTER_BITS). */
+static uint64_t
+subtract_timestamp (uint64_t a, uint64_t b)
+{
+       GLint timestamp_bits;
+
+       glGetQueryiv (GL_TIMESTAMP, GL_QUERY_COUNTER_BITS, &timestamp_bits);
+
+       /* Note: "<<" isn't defined for the number of bits in the
+        * type, and the compiler will punish you.
+        */
+       if (timestamp_bits == 64)
+               return a - b;
+
+       if (b > a)
+               return (1ull << timestamp_bits) + a - b;
+       else
+               return a - b;
+}
+
 metrics_t *
 metrics_create (metrics_info_t *info)
 {
@@ -144,6 +166,9 @@ metrics_create (metrics_info_t *info)
        /* Get the first frame timestamp started immediately. */
        glQueryCounter (metrics->swap_end_timestamp_id, GL_TIMESTAMP);
 
+       /* As well as the initial CPU time. */
+       clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &metrics->cpu_time_ts);
+
        return metrics;
 }
 
@@ -409,6 +434,7 @@ accumulate_program_metrics (metrics_t *metrics, metrics_op_t op,
        {                                                               \
                fprintf (stderr, "Unexpected end-of-buffer while "      \
                         "parsing results\n");                          \
+               value = 0.0;                                            \
                break;                                                  \
        }                                                               \
        (var) = *((typeof(var) *) p);                                   \
@@ -832,9 +858,11 @@ metrics_end_frame_pre_swap (metrics_t *metrics)
                printf ("# frame: Frame_Number Frame_Time_milliseconds Frame_latency_milliseconds CPU_load GPU_load\n");
        } else {
                /* Subtract previous frame's times to get frame times. */
-               frame_time_ns = swap_end_timestamp - metrics->previous_swap_end_timestamp;
+               frame_time_ns = subtract_timestamp (swap_end_timestamp,
+                                                   metrics->previous_swap_end_timestamp);
 
-               latency_ns = swap_end_timestamp - metrics->swap_begin_timestamp;
+               latency_ns = subtract_timestamp (swap_end_timestamp,
+                                                metrics->swap_begin_timestamp);
 
                cpu_time = TIMESPEC_DIFF (metrics->previous_cpu_time_ts, metrics->cpu_time_ts);