Fio latency inconsistent

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Hi

I am trying to understand fio latency numbers.
Would be great if you can clarify why latency numbers are inconsistent.

Here is sample fio output:

read_lat: (g=0): rw=randread, bs=512-512/512-512/512-512,
ioengine=libaio, iodepth=1
fio-2.1.10
Starting 1 thread

read_lat: (groupid=0, jobs=1): err= 0: pid=10848: Mon Jul 11 13:34:27 2016
  read : io=7541.2MB, bw=12870KB/s, iops=25740, runt=600001msec
    slat (usec): min=3, max=62, avg= 3.95, stdev= 0.37
    clat (usec): min=0, max=12053, avg=34.19, stdev=24.21
     lat (usec): min=28, max=12057, avg=38.24, stdev=24.21
    clat percentiles (usec):
     |  1.00th=[   25],  5.00th=[   26], 10.00th=[   26], 20.00th=[   26],
     | 30.00th=[   26], 40.00th=[   26], 50.00th=[   26], 60.00th=[   27],
     | 70.00th=[   27], 80.00th=[   27], 90.00th=[   91], 95.00th=[  106],
     | 99.00th=[  112], 99.50th=[  112], 99.90th=[  118], 99.95th=[  120],
     | 99.99th=[  129]
    bw (KB  /s): min=11701, max=13161, per=100.00%, avg=12870.89, stdev=114.55
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=89.85%, 100=5.02%
    lat (usec) : 250=5.12%, 500=0.01%, 750=0.01%, 1000=0.01%
    lat (msec) : 2=0.01%, 4=0.01%, 10=0.01%, 20=0.01%
  cpu          : usr=5.91%, sys=13.98%, ctx=15444904, majf=0, minf=8
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=15444203/w=0/d=0, short=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
   READ: io=7541.2MB, aggrb=12870KB/s, minb=12870KB/s, maxb=12870KB/s,
mint=600001msec, maxt=600001msec

Disk stats (read/write):
  sdb: ios=15440539/0, merge=0/0, ticks=506729/0, in_queue=504796, util=84.17%



>From output:
Run time = 600001 ms
queue depth = 1
performed IO = 25740

So correct me if i am wrong, but 600001 / 25740 = 23.31 ms
However, fio reports an average latency of 38.24 ms.
Should those numbers be consistent?


Thanks
-- 
Lucas
read_lat: (g=0): rw=randread, bs=512-512/512-512/512-512, ioengine=libaio, iodepth=1
fio-2.1.10
Starting 1 thread

read_lat: (groupid=0, jobs=1): err= 0: pid=10848: Mon Jul 11 13:34:27 2016
  read : io=7541.2MB, bw=12870KB/s, iops=25740, runt=600001msec
    slat (usec): min=3, max=62, avg= 3.95, stdev= 0.37
    clat (usec): min=0, max=12053, avg=34.19, stdev=24.21
     lat (usec): min=28, max=12057, avg=38.24, stdev=24.21
    clat percentiles (usec):
     |  1.00th=[   25],  5.00th=[   26], 10.00th=[   26], 20.00th=[   26],
     | 30.00th=[   26], 40.00th=[   26], 50.00th=[   26], 60.00th=[   27],
     | 70.00th=[   27], 80.00th=[   27], 90.00th=[   91], 95.00th=[  106],
     | 99.00th=[  112], 99.50th=[  112], 99.90th=[  118], 99.95th=[  120],
     | 99.99th=[  129]
    bw (KB  /s): min=11701, max=13161, per=100.00%, avg=12870.89, stdev=114.55
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=89.85%, 100=5.02%
    lat (usec) : 250=5.12%, 500=0.01%, 750=0.01%, 1000=0.01%
    lat (msec) : 2=0.01%, 4=0.01%, 10=0.01%, 20=0.01%
  cpu          : usr=5.91%, sys=13.98%, ctx=15444904, majf=0, minf=8
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=15444203/w=0/d=0, short=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
   READ: io=7541.2MB, aggrb=12870KB/s, minb=12870KB/s, maxb=12870KB/s, mint=600001msec, maxt=600001msec

Disk stats (read/write):
  sdb: ios=15440539/0, merge=0/0, ticks=506729/0, in_queue=504796, util=84.17%

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