From 73df3e072e210c93934d21668cc8adba4ae74d77 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 17 Dec 2014 08:51:23 -0700 Subject: [PATCH 1/1] gettime: offset CPU cycle counter by initial value Should then be safe for the full 2^64 cycles, and we push the more expensive variable division to later in the run (which is probably never). Signed-off-by: Jens Axboe --- gettime.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/gettime.c b/gettime.c index 7e3e2e5b..a95b5452 100644 --- a/gettime.c +++ b/gettime.c @@ -17,6 +17,7 @@ static unsigned long cycles_per_usec; static unsigned long inv_cycles_per_usec; static uint64_t max_cycles_for_mult; +static unsigned long long cycles_start, cycles_wrap; #endif int tsc_reliable = 0; @@ -169,12 +170,16 @@ static void __fio_gettime(struct timeval *tp) uint64_t usecs, t; t = get_cpu_clock(); - if (t < tv->last_cycles && tv->last_tv_valid && - !tv->warned) { - log_err("fio: CPU clock going back in time\n"); - tv->warned = 1; + if (t < cycles_start && !cycles_wrap) + cycles_wrap = 1; + else if (cycles_wrap && t >= cycles_start) { + if (!tv->warned) { + log_err("fio: double CPU clock wrap\n"); + tv->warned = 1; + } } + t -= cycles_start; tv->last_cycles = t; tv->last_tv_valid = 1; #ifdef ARCH_CPU_CLOCK_CYCLES_PER_USEC @@ -299,6 +304,8 @@ static int calibrate_cpu_clock(void) inv_cycles_per_usec = 16777216UL / cycles_per_usec; max_cycles_for_mult = ~0ULL / inv_cycles_per_usec; dprint(FD_TIME, "inv_cycles_per_usec=%lu\n", inv_cycles_per_usec); + cycles_start = get_cpu_clock(); + dprint(FD_TIME, "cycles_start=%llu\n", cycles_start); return 0; } #else -- 2.25.1