On 04/27/2016 02:38 PM, Jens Axboe wrote:
I'll try and see if I can reproduce this.
So I took a look at your logged output. The way that fio logs is that it
does it on IO completion. You have set 1s intervals, so it checks, when
an IO completes, if we're due for logging the previous interval IOPS:
spent = mtime_since(&td->iops_sample_time, t);
if (spent < td->o.iops_avg_time)
return;
If you are doing lots of IO, it matches pretty evenly. But for slow
workloads, it will end up being skewed a bit. It won't be too hard to
fix the drift, though, but it still won't make it clock precise at exact
1s intervals.
We could move this part into the main thread, and out of the workers.
Then we could make it more precise. Might not be a bad idea in general,
since it'll move some of this code out of the fast path.
I'll take a stab at it.
--
Jens Axboe
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