On Mon, May 27 2013, sampath rapaka wrote: > hi > > i have run couple of fio runs. i am running this over raid1 device. i > have captured blktrace for each run. I was going through the > blktraces. what i have observed is there instances where there is > commit happening to disk at say time stamp X. I was expecting a new IO > to be submitted at X+1 time stamp. but i see next IO is submitted at > time stamp Y. > > Y-X is more than 1. Is there any delay introduced from FIO between two > fios. or what could be the probable reasons to see such delay? let me > know if my understanding is wrong. > > Below is the excerpt from blktrace: > > 21378 8,32 3 9162 0.116015463 0 C WS 574576152 + 8 [0] > 21379 8,16 3 10690 0.116020386 0 C WS 574576152 + 8 [0] > 21380 9,0 0 1 0.120074779 8797 Q WS 131300520 + 8 [fitness] > > from lines 21379(C) to 21380(Q) there is lots of delay for submission of new IO. > > So i was thinking in lines of any delay from FIO between submissions > of IO or they submit IO as soon as it is available. > > Question 2: > I have also observed larger delays in Q-D values. which is more than D-C value. > > What could be the possible reasons for this behavior ? Fio doesn't introduce any delays on purpose. What job file are you running? It could either be that fio is scheduled out or in other ways in a non-running state. Or perhaps fio is waiting for completions. Line 21380 above is something called 'fitness', what is that? -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
