On 2012-12-20 01:52, Sam Bradshaw wrote:
>
> This patch generally converts a division to a subtraction in fio_gettime().
>
> Shows ~1% better iops with synthetic benchmarking at roughly the same cpu
> time spent in fio_gettime().
>
> Signed-off-by: Sam Bradshaw <sbradshaw@xxxxxxxxxx>
>
> diff --git a/gettime.c b/gettime.c
> index 248f146..e2a6241 100644
> --- a/gettime.c
> +++ b/gettime.c
> @@ -163,17 +163,23 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
> }
> #ifdef ARCH_HAVE_CPU_CLOCK
> case CS_CPUCLOCK: {
> - unsigned long long usecs, t;
> + unsigned long long usecs, t, delta = 0;
>
> t = get_cpu_clock();
> if (tv && t < tv->last_cycles) {
> dprint(FD_TIME, "CPU clock going back in time\n");
> t = tv->last_cycles;
> - } else if (tv)
> + } else if (tv) {
> + if (tv->last_tv_valid)
> + delta = t - tv->last_cycles;
> tv->last_cycles = t;
> + }
>
> usecs = t / cycles_per_usec;
> - tp->tv_sec = usecs / 1000000;
> + if (delta > 1000000)
> + tp->tv_sec = tv->last_tv.tv_sec;
> + else
> + tp->tv_sec = usecs / 1000000;
Shouldn't that be delta < 1000000? What am I missing? If the diff is
more than 1M usecs, then do the division. If not, we can reuse the
seconds from the last one.
--
Jens Axboe
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