Re: Generating almost-sequential traffic

[Jens Axboe <axboe@kernel.dk>]

On Thu, Jun 27 2013, Carl Zwanzig wrote:
> > From: Jens Axboe [mailto:axboe@kernel.dk]
> > Sent: Thursday, June 27, 2013 2:01 AM
> 
> > See percentage_random in the man page (or --cmdhelp=percentage_random)
> 
> In the tests I'm running, the sequence has to continue essentially
> uninterrupted with the occasional drop/transposition, but it can't
> contain LBAs that are wildly off. So '1 2 3 (4) 5 6' or '1 2 3 (5 4)
> 6' are good, '1 2 3 9999 4 5 6' is not. They trigger different
> specific behaviors in some hard drives.
> 
> Is there a good place in the code to insert this sort or thing?

I would look at the profile support in fio. That allows you to hook into
io_u.c:get_next_offset(), which is where fio decides what the next
offset should be. If a profile defines ops->fill_io_u(), then that is
called instead. That gives you absolute control of the IO pattern,
without having to modify core fio code.

-- 
Jens Axboe