Re: fio serialize across jobs

[Jens Axboe <axboe@kernel.dk>]

General comments on this... Fio does have a notion of having multiple
workers per state, most notably for the offload IO model (io_submit_mode).
That would make ethe most sense to utilize for something like this,
rather than having independent jobs that need to share basically everything.
You end up with a rather large rework, only to arrive at what the offload
IO model can already do.


On 7/9/18 11:58 AM, Jeff Furlong wrote:
> What if we limited the jobs to 2 and limited the second job's QD to 1?  Might that limit the locking overhead?
> 
> Regards,
> Jeff
> 
> -----Original Message-----
> From: Sitsofe Wheeler [mailto:sitsofe@gmail.com] 
> Sent: Friday, July 6, 2018 9:23 PM
> To: Jeff Furlong <jeff.furlong@wdc.com>
> Cc: fio@vger.kernel.org
> Subject: Re: fio serialize across jobs
> 
> Hi,
> 
> On 6 July 2018 at 23:14, Jeff Furlong <jeff.furlong@wdc.com> wrote:
>> Hi All,
>> Back in commit 997b5680d139ce82c2034ba3a0d602cfd778b89b "fio: add serialize_overlap option" the feature was added to prevent write/trim race conditions within the queue.  Can this feature be applied to multiple jobs?  Consider:
>>
>> fio --ioengine=libaio --direct=1  --filename=/dev/nvme0n1 --time_based 
>> --name=test1 --rw=randwrite --runtime=5s --name=test2 --rw=randwrite 
>> --runtime=5s --serialize_overlap=1
>>
>> Would we have to call in_flight_overlap() in a loop with all thread data pointers?
> 
> It would be a be more work (the original serialize_overlap was fiddly to make correct but was easy to get going) but I can see why you might want what you describe. The big problem is that I can't see how you can do it without introducing a large amount of locking into the fio's I/O path. I think this would also border on a feature that diskspd has where multiple threads can do I/O to a single file but they all share a randommap...
> 
> --
> Sitsofe | http://sucs.org/~sits/
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> 


-- 
Jens Axboe