On 03/19/2015 11:34 AM, Tejun Heo wrote:
> Hello,
>
> So, Jens noticed that fio process exiting takes seconds when there are
> multiple aio contexts and the culprit seems to be the serial
> percpu_ref draining in exit_aio().  It's generally a bad idea to
> expose RCU latencies to userland because they add up really quickly
> and are unrelated to other performance parameters.  Can you guys
> please at least update the code so that it waits for all percpu_refs
> to drain at the same time rather than one after another?  That should
> resolve the worst part of the problem.

This works for me. Before:

real	0m5.872s
user	0m0.020s
sys	0m0.040s

after

real	0m0.246s
user	0m0.020s
sys	0m0.040s

It solves the exit_aio() issue, but if the app calls io_destroy(), then 
we are back to square one...

-- 
Jens Axboe