Fio regression caused by f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94

["Lukáš Doktor" <ldoktor@redhat.com>]

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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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