Shouldn't `--group_reporting` be used?

[RJVB]

• KDiskMark Version: 3.2.0
• FIO Version: fio-fio-3.41-110-g1a04e5

Description:

Looking at the fio output and manpage I see that there is a way to make it generate output with the averages over all jobs (aka multi-thread tests) that can be compared directly with the output from single-threaded tests. I haven't yet found any indication in the KDiskMark code that any kind of averaging or aggregation is done in this case, so wouldn't it be better to add the --group_reporting option? It does make a difference (and can be used with numjobs=1 safely).

NB: on Linux (and Darwin), fio spawns separate processes, so the term "Threads" is misleading here!

[RJVB]

Here are some results with 3 different I/O engines, using my own fork which adds that option, and adapts the test parameters smartly in case of known limitations on the maximum possible number of queues.
Drive is a 256Gb Kingston SKC600MS drive mounted over USB3, with a whole-device XFS filesystem on it, the host a lowly notebook with a 4-core N3150 CPU.

Interestingly, fio's default I/O engine "psync" (which uses plain & simple read() and write() calls) performs on-par with or even slightly better than the libaio engine.

With libaio:

                        KDiskMark (3.2.0): https://github.com/JonMagon/KDiskMark
  Flexible I/O Tester (fio-3.41-110-g1a04e5-dirty): https://github.com/axboe/fio
--------------------------------------------------------------------------------
* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes

[Read]
Sequential 256 KiB (Q=  8, T= 1):   370.216 MB/s [   1446.2 IOPS] <  5391.83 us>
Sequential 256 KiB (Q=  1, T= 1):   266.818 MB/s [   1042.3 IOPS] <   812.71 us>
    Random   4 KiB (Q= 32, T= 1):   106.849 MB/s [  26712.3 IOPS] <  1164.72 us>
    Random   4 KiB (Q=  1, T= 1):    18.174 MB/s [   4543.5 IOPS] <   159.05 us>

[Write]
Sequential 256 KiB (Q=  8, T= 1):   430.040 MB/s [   1679.8 IOPS] <  4546.93 us>
Sequential 256 KiB (Q=  1, T= 1):   236.931 MB/s [    925.5 IOPS] <   830.01 us>
    Random   4 KiB (Q= 32, T= 1):    87.854 MB/s [  21963.6 IOPS] <  1416.09 us>
    Random   4 KiB (Q=  1, T= 1):    24.304 MB/s [   6076.2 IOPS] <   112.30 us>

[Mix] Read 70%/Write 30%
Sequential 256 KiB (Q=  8, T= 1):   146.346 MB/s [    571.7 IOPS] <  7995.81 us>
Sequential 256 KiB (Q=  1, T= 1):   113.287 MB/s [    442.5 IOPS] <  1097.76 us>
    Random   4 KiB (Q= 32, T= 1):    54.196 MB/s [  13549.0 IOPS] <  1330.56 us>
    Random   4 KiB (Q=  1, T= 1):    10.854 MB/s [   2713.7 IOPS] <   149.45 us>

Profile: Default [+Mix]
 Engine: fio-libaio
   Test: 1 GiB (x3) [Measure: 10 sec / Interval: 5 sec]
   Date: 2026-02-25 18:23:40
     OS: ubuntu 14.04 [linux 4.14.328-ck1-westmere-rjvb]
 Target: /mnt 0% (0.27/238.36 GiB)

With posixaio:

                        KDiskMark (3.2.0): https://github.com/JonMagon/KDiskMark
  Flexible I/O Tester (fio-3.41-110-g1a04e5-dirty): https://github.com/axboe/fio
--------------------------------------------------------------------------------
* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes

[Read]
Sequential 256 KiB (Q=  8, T= 1):   261.430 MB/s [   1021.2 IOPS] <  7816.43 us>
Sequential 256 KiB (Q=  1, T= 1):   249.010 MB/s [    972.7 IOPS] <   998.60 us>
    Random   4 KiB (Q= 32, T= 1):    19.017 MB/s [   4754.4 IOPS] <  6688.01 us>
    Random   4 KiB (Q=  1, T= 1):    16.215 MB/s [   4053.8 IOPS] <   228.65 us>

[Write]
Sequential 256 KiB (Q=  8, T= 1):   292.544 MB/s [   1142.8 IOPS] <  6879.09 us>
Sequential 256 KiB (Q=  1, T= 1):   226.531 MB/s [    884.9 IOPS] <   994.96 us>
    Random   4 KiB (Q= 32, T= 1):    26.440 MB/s [   6610.3 IOPS] <  4787.98 us>
    Random   4 KiB (Q=  1, T= 1):    21.371 MB/s [   5342.9 IOPS] <   169.71 us>

[Mix] Read 70%/Write 30%
Sequential 256 KiB (Q=  8, T= 1):   115.547 MB/s [    451.4 IOPS] < 10272.28 us>
Sequential 256 KiB (Q=  1, T= 1):   113.121 MB/s [    441.9 IOPS] <  1252.40 us>
    Random   4 KiB (Q= 32, T= 1):    11.947 MB/s [   2987.0 IOPS] <  6159.25 us>
    Random   4 KiB (Q=  1, T= 1):    10.105 MB/s [   2526.4 IOPS] <   211.31 us>

Profile: Default [+Mix]
 Engine: fio-posixaio
   Test: 1 GiB (x3) [Measure: 10 sec / Interval: 5 sec]
   Date: 2026-02-25 18:41:07
     OS: ubuntu 14.04 [linux 4.14.328-ck1-westmere-rjvb]
 Target: /mnt 0% (0.27/238.36 GiB)

with "psync":

                        KDiskMark (3.2.0): https://github.com/JonMagon/KDiskMark
  Flexible I/O Tester (fio-3.41-110-g1a04e5-dirty): https://github.com/axboe/fio
--------------------------------------------------------------------------------
* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes

[Read]
Sequential 256 KiB (Q=  1, T= 8):   366.051 MB/s [   1429.9 IOPS] <  5579.44 us>
Sequential 256 KiB (Q=  1, T= 1):   280.601 MB/s [   1096.1 IOPS] <   900.84 us>
    Random   4 KiB (Q=  1, T=32):   121.741 MB/s [  30435.3 IOPS] <  1098.53 us>
    Random   4 KiB (Q=  1, T= 1):    20.925 MB/s [   5231.4 IOPS] <   184.37 us>

[Write]
Sequential 256 KiB (Q=  1, T= 8):   431.819 MB/s [   1686.8 IOPS] <  4596.36 us>
Sequential 256 KiB (Q=  1, T= 1):   255.833 MB/s [    999.3 IOPS] <   891.45 us>
    Random   4 KiB (Q=  1, T=32):   127.548 MB/s [  31887.0 IOPS] <   978.16 us>
    Random   4 KiB (Q=  1, T= 1):    27.457 MB/s [   6864.2 IOPS] <   137.51 us>

[Mix] Read 70%/Write 30%
Sequential 256 KiB (Q=  1, T= 8):   146.000 MB/s [    570.3 IOPS] <  8120.33 us>
Sequential 256 KiB (Q=  1, T= 1):   116.174 MB/s [    453.8 IOPS] <  1242.26 us>
    Random   4 KiB (Q=  1, T=32):    73.244 MB/s [  18311.1 IOPS] <  1000.29 us>
    Random   4 KiB (Q=  1, T= 1):    12.601 MB/s [   3150.3 IOPS] <   176.14 us>

Profile: Default [+Mix]
 Engine: fio-default
   Test: 1 GiB (x3) [Measure: 10 sec / Interval: 5 sec]
   Date: 2026-02-25 19:06:09
     OS: ubuntu 14.04 [linux 4.14.328-ck1-westmere-rjvb]
 Target: /mnt 0% (0.27/238.36 GiB)