hi jens
Firstly sorry for misplacing the logs in the above mail. Those are
excerpts from other test program.
Thanks for your clarification.
FIO Job File is some thing like this :
3 [global]
4 ioengine=libaio
5 direct=1
6 filename=/dev/md0
7 blocksize=4k
8 iodepth=${IoDepth}
9 size=${Size}
10 write_iops_log=total_iops_W9R1
11
12 [read1]
13 rw=randread
14 write_lat_log=read1_W9R1
15
16
17 [write1]
18 rw=randwrite
19 write_lat_log=write1_W9R1
20
21 [write2]
22 rw=randwrite
23 write_lat_log=write2_W9R1
Below is the log from blktrace:
1163147 8,16 0 172181 2.386764602 0 C WS 872560 + 8
[0] >> This is where commit to 8,16 happens
1163148 8,16 0 172182 2.386767040 0 D WS 2244224 + 8 [swapper/0]
1163149 8,32 0 269041 2.388917654 0 C WS 4992504 + 8 [0]
1163150 8,32 0 269042 2.388923411 0 D WS 3160896 + 8 [swapper/0]
1163151 9,0 0 20654 2.388933229 22220 Q WS 4514832 + 8
[fio] >> This is where new IO is Queued
1163152 8,16 3 159545 2.388938315 21059 Q WS 4776976 + 8
[md0_raid1_slow0]
1163153 8,16 3 159546 2.388938804 21059 G WS 4776976 + 8
[md0_raid1_slow0]
Gap between those lines seems to be big. So i was wondering whether
any Delay is introduced by FIO.
I have one more question in general though not related to above logs.
Increasing the nr_request value for a device(some thousands) results
in increase in Q-D values for a IO while having queue depth at 31?
echo 10000 > /sys/block/sdb/queue/nr_requests
echo 31 > /sys/block/sdb/device/queue_depth
regards
sampath
On Mon, May 27, 2013 at 7:03 PM, Jens Axboe <axboe@xxxxxxxxx> wrote:
> 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
>
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