Re: [PATCH] fio: fix hangs due to iodepth_low

[Jens Axboe <axboe@kernel.dk>]

On 2014-09-03 18:23, Robert Elliott wrote:
> With some combinations of iodepth, iodepth_batch, iodepth_batch_complete,
> and io_depth_low, do_io hangs after reaping the first set of completions
> since io_u_queued_complete is called requesting more completions than
> td->cur_depth.
>
> Example printing min_evts and td->cur_depth in the do/while loop:
> waiting on min=96 cd=627
> waiting on min=96 cd=531
> waiting on min=96 cd=435
> waiting on min=96 cd=339
> waiting on min=96 cd=243
> waiting on min=96 cd=147
> waiting on min=96 cd=51
> Jobs: 12 (f=12): [r(12)] [43.8% done] [0KB/0KB/0KB /s] [0/0/0 iops] [eta 00m:09s]
> ...
> Jobs: 12 (f=12): [r(12)] [0.0% done] [0KB/0KB/0KB /s] [0/0/0 iops] [eta 2863d:18h:28m:38s]
> <fio never exits>
>
> Fix this by adjusting min_evts to the current_depth if that is smaller.
>
> Tested with a jobfile including:
> iodepth=1011
> iodepth_batch=96
> iodepth_batch_complete=96
> iodepth_low=1
> runtime=15
> time_based
>
> Made the same change to do_verify, but not tested there.
>
> Signed-off-by: Robert Elliott <elliott@hp.com>
> ---
>   backend.c |    4 ++++
>   1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/backend.c b/backend.c
> index 7cb0a39..ce97f6d 100644
> --- a/backend.c
> +++ b/backend.c
> @@ -606,6 +606,8 @@ reap:
>   				 * and do the verification on them through
>   				 * the callback handler
>   				 */
> +				if (min_events < td->cur_depth)
> +					min_events = td->cur_depth;

Did you reverse these? From the description and debug output, seems it 
should be:

	if (min_events > td->cur_depth)
		min_events = td->cur_depth;

and we should probably put this logic in io_u_queued_complete(), I think 
that would be a safer alternative instead of near the callers.

-- 
Jens Axboe