gettime: even rounding, don't always round up

[fio.git] / gettime.c

diff --git a/gettime.c b/gettime.c
index 921c171fdef80a414e8fdf039c9c09faefa30e02..3011d7440738c050fc5ae696720e97bf896926bd 100644 (file)
--- a/gettime.c
+++ b/gettime.c
@@ -15,13 +15,14 @@
 
 #ifdef ARCH_HAVE_CPU_CLOCK
 static unsigned long cycles_per_usec;
-static unsigned long last_cycles;
-int tsc_reliable = 0;
+static unsigned long inv_cycles_per_usec;
 #endif
+int tsc_reliable = 0;
 
 struct tv_valid {
        struct timeval last_tv;
        int last_tv_valid;
+       unsigned long last_cycles;
 };
 static pthread_key_t tv_tls_key;
 
@@ -120,13 +121,22 @@ static void fio_init gtod_init(void)
 
 #endif /* FIO_DEBUG_TIME */
 
+static int fill_clock_gettime(struct timespec *ts)
+{
+#ifdef FIO_HAVE_CLOCK_MONOTONIC
+       return clock_gettime(CLOCK_MONOTONIC, ts);
+#else
+       return clock_gettime(CLOCK_REALTIME, ts);
+#endif
+}
+
 #ifdef FIO_DEBUG_TIME
 void fio_gettime(struct timeval *tp, void *caller)
 #else
 void fio_gettime(struct timeval *tp, void fio_unused *caller)
 #endif
 {
-       struct tv_valid *t;
+       struct tv_valid *tv;
 
 #ifdef FIO_DEBUG_TIME
        if (!caller)
@@ -139,6 +149,8 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
                return;
        }
 
+       tv = pthread_getspecific(tv_tls_key);
+
        switch (fio_clock_source) {
        case CS_GTOD:
                gettimeofday(tp, NULL);
@@ -146,11 +158,7 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
        case CS_CGETTIME: {
                struct timespec ts;
 
-#ifdef FIO_HAVE_CLOCK_MONOTONIC
-               if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0) {
-#else
-               if (clock_gettime(CLOCK_REALTIME, &ts) < 0) {
-#endif
+               if (fill_clock_gettime(&ts) < 0) {
                        log_err("fio: clock_gettime fails\n");
                        assert(0);
                }
@@ -164,15 +172,15 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
                unsigned long long usecs, t;
 
                t = get_cpu_clock();
-               if (t < last_cycles) {
+               if (tv && t < tv->last_cycles) {
                        dprint(FD_TIME, "CPU clock going back in time\n");
-                       t = last_cycles;
-               }
+                       t = tv->last_cycles;
+               } else if (tv)
+                       tv->last_cycles = t;
 
-               usecs = t / cycles_per_usec;
+               usecs = (t * inv_cycles_per_usec) / 16777216UL;
                tp->tv_sec = usecs / 1000000;
                tp->tv_usec = usecs % 1000000;
-               last_cycles = t;
                break;
                }
 #endif
@@ -185,32 +193,38 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
         * If Linux is using the tsc clock on non-synced processors,
         * sometimes time can appear to drift backwards. Fix that up.
         */
-       t = pthread_getspecific(tv_tls_key);
-       if (t) {
-               if (t->last_tv_valid) {
-                       if (tp->tv_sec < t->last_tv.tv_sec)
-                               tp->tv_sec = t->last_tv.tv_sec;
-                       else if (t->last_tv.tv_sec == tp->tv_sec &&
-                                tp->tv_usec < t->last_tv.tv_usec)
-                               tp->tv_usec = t->last_tv.tv_usec;
+       if (tv) {
+               if (tv->last_tv_valid) {
+                       if (tp->tv_sec < tv->last_tv.tv_sec)
+                               tp->tv_sec = tv->last_tv.tv_sec;
+                       else if (tv->last_tv.tv_sec == tp->tv_sec &&
+                                tp->tv_usec < tv->last_tv.tv_usec)
+                               tp->tv_usec = tv->last_tv.tv_usec;
                }
-               t->last_tv_valid = 1;
-               memcpy(&t->last_tv, tp, sizeof(*tp));
+               tv->last_tv_valid = 1;
+               memcpy(&tv->last_tv, tp, sizeof(*tp));
        }
 }
 
 #ifdef ARCH_HAVE_CPU_CLOCK
 static unsigned long get_cycles_per_usec(void)
 {
+       struct timespec ts;
        struct timeval s, e;
        unsigned long long c_s, c_e;
 
-       gettimeofday(&s, NULL);
+       fill_clock_gettime(&ts);
+       s.tv_sec = ts.tv_sec;
+       s.tv_usec = ts.tv_nsec / 1000;
+
        c_s = get_cpu_clock();
        do {
                unsigned long long elapsed;
 
-               gettimeofday(&e, NULL);
+               fill_clock_gettime(&ts);
+               e.tv_sec = ts.tv_sec;
+               e.tv_usec = ts.tv_nsec / 1000;
+
                elapsed = utime_since(&s, &e);
                if (elapsed >= 1280) {
                        c_e = get_cpu_clock();
@@ -259,11 +273,13 @@ static void calibrate_cpu_clock(void)
                dprint(FD_TIME, "cycles[%d]=%lu\n", i, cycles[i] / 10);
 
        avg /= samples;
-       avg = (avg + 9) / 10;
+       avg = (avg + 5) / 10;
        dprint(FD_TIME, "avg: %lu\n", avg);
        dprint(FD_TIME, "mean=%f, S=%f\n", mean, S);
 
        cycles_per_usec = avg;
+       inv_cycles_per_usec = 16777216UL / cycles_per_usec;
+       dprint(FD_TIME, "inv_cycles_per_usec=%lu\n", inv_cycles_per_usec);
 }
 #else
 static void calibrate_cpu_clock(void)