Fio version 3.1 on CentOS - Possible bug reporting

Fio version 3.1 on CentOS - Possible bug reporting

[Kailash Mallikarjunaswamy]

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Hi,



I am writing to report a possible* bug on:



fio version - 3.1

Operating System - CentOS  7.6.1810

kernel: 3.10.0-957.1.3.el7.x86_64



I use a HP Proliant Enterprise Server hardware to run the metrics



Bug: In some of the runs, the max value of completion latency (clat) is lesser than the 9-nines percentile value. How is this possible? I have marked the numbers in red below. Kindly take a look.

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Workload:



sudo chrt -f 1 fio  --filename=/dev/nvme0n1 --numjobs=1 --iodepth=512 --offset=0M --bs=

7681501126656 --size=

7681501126656 --io_size=%s --rw=read --buffered=0 --thread --time_based --runtime=60 --name=seqtest0 --group_reporting --disable_lat=1 --disable_slat=1 --disable_bw_measurement=1 --zero_buffers --ioengine=libaio --percentile=99:99.9:99.99:99.999:99.9999:99.99999:99.999999:99.9999999 --output-format=json,normal --eta=never --invalidate=1 --end_fsync=0 --refill_buffers



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Result:



seqtest0: (groupid=0, jobs=1): err= 0: pid=3908: Tue Feb 26 18:02:25 2019
   read: IOPS=25.1k, BW=3135MiB/s (3287MB/s)(184GiB/60021msec)
    clat (usec): min=16426, max=41005, avg=20384.67, stdev=337.20
    clat percentiles (usec):
     | 99.0000000th=[20579], 99.9000000th=[21103], 99.9900000th=[38011],
     | 99.9990000th=[40633], 99.9999000th=[41157], 99.9999900th=[41157],
     | 99.9999990th=[41157], 99.9999999th=[41157]
   bw (  MiB/s): min= 2981, max= 3144, per=100.00%, avg=3135.58, stdev=14.46, samples=120
   iops        : min=23848, max=25154, avg=25084.63, stdev=115.65, samples=120
  lat (msec)   : 20=0.31%, 50=99.69%
  cpu          : usr=4.10%, sys=64.00%, ctx=742962, majf=0, minf=44
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=100.0%
     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=0.1%
     issued rwt: total=1505214,0,0, short=0,0,0, dropped=0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=512

Run status group 0 (all jobs):
   READ: bw=3135MiB/s (3287MB/s), 3135MiB/s-3135MiB/s (3287MB/s-3287MB/s), io=184GiB (197GB), run=60021-60021msec

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Any inputs/help will be greatly appreciated.



Thanks in advance!



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