On 12/20/2012 12:14 AM, Jens Axboe wrote:
> 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.
>
Yes, my bad. Correct patch below.
diff --git a/gettime.c b/gettime.c
index 035d275..89f3e27 100644
--- a/gettime.c
+++ b/gettime.c
@@ -168,17 +168,23 @@ 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 && delta < 1000000)
+ tp->tv_sec = tv->last_tv.tv_sec;
+ else
+ tp->tv_sec = usecs / 1000000;
tp->tv_usec = usecs % 1000000;
break;
}
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