Fio regression caused by f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94

[Lukáš Doktor]

Hello Mike, Paolo, others,

in my perf pipeline I noticed a regression bisected to the 
f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94 - "thread-posix: remove the posix 
semaphore support" commit and I'd like to ask you to verify it might have 
caused that and eventually consider fixing it. The regression is visible, 
reproducible and clearly bisectable to this commit with the following 2 
scenarios:

1. fio write 4KiB using the nbd ioengine on localhost
2. fio read 4KiB using #cpu jobs and iodepth=8 on a rotational disk using qcow2 
image and default virt-install 

    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source 
file="/var/lib/libvirt/images/RHEL-8.4.0-20210503.1-virtlab506.DefaultLibvirt0.qcow2"/>
      <target dev="vda" bus="virtio"/>
    </disk>

but smaller regressions can be seen under other scenarios as well since this 
commit. You can find the report from bisections here:

https://ldoktor.github.io/tmp/RedHat-virtlab506/v7.0.0/RedHat-virtlab506-f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94-RHEL-8.4.0-20210503.1-1.html
https://ldoktor.github.io/tmp/RedHat-virtlab506/v7.0.0/RedHat-virtlab506-f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94-RHEL-8.4.0-20210503.1-2.html

Regards,
Lukáš

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