gettime: add some sanity checks to platform clock

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/gettime.c b/gettime.c
index 5b85a23b8519f3ca2bf1bde102972f4bf648377b..d56045c58919812df17d46dd8148b78471810190 100644 (file)
--- a/gettime.c
+++ b/gettime.c
@@ -262,7 +262,7 @@ static unsigned long get_cycles_per_usec(void)
 
 #define NR_TIME_ITERS  50
 
-static void calibrate_cpu_clock(void)
+static int calibrate_cpu_clock(void)
 {
        double delta, mean, S;
        uint64_t avg, cycles[NR_TIME_ITERS];
@@ -279,6 +279,13 @@ static void calibrate_cpu_clock(void)
                }
        }
 
+       /*
+        * The most common platform clock breakage is returning zero
+        * indefinitely. Check for that and return failure.
+        */
+       if (!cycles[0] && !cycles[NR_TIME_ITERS - 1])
+               return 1;
+
        S = sqrt(S / (NR_TIME_ITERS - 1.0));
 
        samples = avg = 0;
@@ -305,10 +312,12 @@ static void calibrate_cpu_clock(void)
        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);
+       return 0;
 }
 #else
-static void calibrate_cpu_clock(void)
+static int calibrate_cpu_clock(void)
 {
+       return 1;
 }
 #endif
 
@@ -343,7 +352,9 @@ void fio_clock_init(void)
 #endif
 
        fio_clock_source_inited = fio_clock_source;
-       calibrate_cpu_clock();
+
+       if (calibrate_cpu_clock())
+               tsc_reliable = 0;
 
        /*
         * If the arch sets tsc_reliable != 0, then it must be good enough
@@ -481,6 +492,13 @@ static void *clock_thread_fn(void *data)
        }
 
        log_info("cs: cpu%3d: %lu clocks seen\n", t->cpu, t->entries[CLOCK_ENTRIES - 1].tsc - t->entries[0].tsc);
+       /*
+        * The most common platform clock breakage is returning zero
+        * indefinitely. Check for that and return failure.
+        */
+       if (!t->entries[CLOCK_ENTRIES - 1].tsc && !t->entries[0].tsc)
+               return (void *) 1;
+
        return NULL;
 }