Re: [PATCH 2/2] init: force threads when checking overlap in offload mode

[Jens Axboe <axboe@kernel.dk>]

On 10/16/18 9:33 AM, Vincent Fu wrote:
> On 10/16/2018 11:29 AM, Jens Axboe wrote:
>> On 10/16/18 9:26 AM, vincentfu@gmail.com wrote:
>>> From: Vincent Fu <vincent.fu@wdc.com>
>>>
>>> serialize_overlap combined with io_submit_mode=offload requires
>>> threads. Print a warning and force the use of threads if the user
>>> did not specify threads.
>> Why does it require threads? Is it because of the use of a pthread
>> mutex? If so, that should just be a fio mutex instead, and you would
>> not have this restrictions (on most platforms, at least).
>>
> It requires threads because io_u's are not allocated from the shared
> memory area. Jobs need to access each other's io_u's to check for overlap.

Gotcha. Might be better to change that rather than impose limitations
on needing threads for this specific configuration.

Probably make it dependent on offload and serialize_overlap for now,
it'd be less risky. The risk here being that higher queue depth
jobs running out of memory in the smalloc pool.

-- 
Jens Axboe