What were you trying to do that didn't work?
The disk performance with an IOthread is worse than without any IOthreads.

Please provide the package NVR for which bug is seen:
Qemu-kvm-8.1.0-3.el9
Kernel-5.14.0-397.el9.x86_64

Host env:

1. lspci | grep NVMe
   cb:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller 172Xa/172Xb (rev 01)
2. cat /sys/bus/pci/devices/0000\:cb\:00.0/numa_node 
   1

1. lscpu 
   Architecture:            x86_64
     CPU op-mode(s):        32-bit, 64-bit
     Address sizes:         46 bits physical, 57 bits virtual
     Byte Order:            Little Endian
   CPU(s):                  96
     On-line CPU(s) list:   0-95
   Vendor ID:               GenuineIntel
     BIOS Vendor ID:        Intel
     Model name:            Intel(R) Xeon(R) Gold 6442Y
       BIOS Model name:     Intel(R) Xeon(R) Gold 6442Y
       CPU family:          6
       Model:               143
       Thread(s) per core:  2
       Core(s) per socket:  24
       Socket(s):           2
       Stepping:            8
       CPU max MHz:         4000.0000
       CPU min MHz:         800.0000
       BogoMIPS:            5200.00
       Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm
                             constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx 
                            smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowp
                            refetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 invpcid_single cdp_l2 ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fs
                            gsbase tsc_adjust sgx bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd sha_n
                            i avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local split_lock_detect avx_vnni avx512_bf16 wbnoinvd
                             dtherm ida arat pln pts hfi vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme avx512_vpopcntdq
                             la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd sgx_lc fsrm md_clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_
                            tile amx_int8 flush_l1d arch_capabilities
   Virtualization features: 
     Virtualization:        VT-x
   Caches (sum of all):     
     L1d:                   2.3 MiB (48 instances)
     L1i:                   1.5 MiB (48 instances)
     L2:                    96 MiB (48 instances)
     L3:                    120 MiB (2 instances)
   NUMA:                    
     NUMA node(s):          2
     NUMA node0 CPU(s):     0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,92,94
     NUMA node1 CPU(s):     1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95
   Vulnerabilities:         
     Gather data sampling:  Not affected
     Itlb multihit:         Not affected
     L1tf:                  Not affected
     Mds:                   Not affected
     Meltdown:              Not affected
     Mmio stale data:       Not affected
     Retbleed:              Not affected
     Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
     Spectre v1:            Mitigation; usercopy/swapgs barriers and __user pointer sanitization
     Spectre v2:            Mitigation; Enhanced / Automatic IBRS, IBPB conditional, RSB filling, PBRSB-eIBRS SW sequence
     Srbds:                 Not affected
     Tsx async abort:       Not affected

1. lsblk 
   NAME                           MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
   sda                              8:0    0 893.8G  0 disk 
   ├─sda1                           8:1    0   600M  0 part /boot/efi
   ├─sda2                           8:2    0     1G  0 part /boot
   └─sda3                           8:3    0 892.2G  0 part 
     ├─rhel_dell-per760-02-root 253:0    0    70G  0 lvm  /
     ├─rhel_dell-per760-02-swap 253:1    0     4G  0 lvm  [SWAP]
     └─rhel_dell-per760-02-home 253:2    0 818.2G  0 lvm  /home
   nvme0n1                        259:0    0 745.2G  0 disk 

1. free -h
                  total        used        free      shared  buff/cache   available
   Mem:           242Gi       3.0Gi       226Gi        18Mi        15Gi       239Gi
   Swap:          4.0Gi          0B       4.0Gi

How reproducible:
100%

Steps to reproduce
Baseline: no iothread
1.bootup a guest with the nvme host diks as data disk and vcpus are pinned to host cpus
<domain type="kvm" xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>rhel</name>
  <uuid>268a093f-b867-4a6c-8fec-1d58aee7e7fa</uuid>
  <memory>2097152</memory>
  <currentMemory>2097152</currentMemory>
  <iothreads>1</iothreads>
  <vcpu placement='static' cpuset="1,3,5,7,9,11,13,15">8</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='1'/>
    <vcpupin vcpu='1' cpuset='3'/>
    <vcpupin vcpu='2' cpuset='5'/>
    <vcpupin vcpu='3' cpuset='7'/>
    <vcpupin vcpu='4' cpuset='9'/>
    <vcpupin vcpu='5' cpuset='11'/>
    <vcpupin vcpu='6' cpuset='13'/>
    <vcpupin vcpu='7' cpuset='15'/>
    <emulatorpin cpuset='17'/>
    <iothreadpin iothread='1' cpuset='19'/>
  </cputune>
  <os firmware="efi">
    <type arch="x86_64" machine="q35">hvm</type>
    <boot dev="hd"/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <kvm>
      <hint-dedicated state='on'/>
      <poll-control state='on'/>
    </kvm>
  </features>
  <cpu mode='host-passthrough' check='partial'>
    <model fallback='allow'/>
  </cpu>
  <clock offset="utc">
    <timer name="rtc" tickpolicy="catchup"/>
    <timer name="pit" tickpolicy="delay"/>
    <timer name="hpet" present="no"/>
  </clock>
  <pm>
    <suspend-to-mem enabled="no"/>
    <suspend-to-disk enabled="no"/>
  </pm>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source file="/home/timao/perf/rhel900-64-virtio-ovmf.qcow2"/>
      <target dev="vda" bus="virtio"/>
    </disk>
    <controller type="usb" model="ich9-ehci1"/>
    <controller type="usb" model="ich9-uhci1">
      <master startport="0"/>
    </controller>
    <controller type="usb" model="ich9-uhci2">
      <master startport="2"/>
    </controller>
    <controller type="usb" model="ich9-uhci3">
      <master startport="4"/>
    </controller>
    <controller type="pci" model="pcie-root"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <controller type="pci" model="pcie-root-port"/>
    <interface type="bridge">
      <source bridge="switch"/>
      <mac address="52:54:00:02:13:36"/>
      <model type="e1000e"/>
    </interface>
    <console type="pty"/>
    <input type="tablet" bus="usb"/>
    <tpm model="tpm-crb">
      <backend type="emulator"/>
    </tpm>
    <graphics type="vnc" port="-1"/>
    <video>
      <model type="bochs"/>
    </video>
  </devices>
  <qemu:commandline>
    <qemu:arg value='-blockdev'/>
    <qemu:arg value='{"driver":"host_device","filename":"/dev/nvme0n1","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}'/>
    <qemu:arg value='-blockdev'/>
    <qemu:arg value='{"node-name":"libvirt-2-format","read-only":false,"driver":"raw","file":"libvirt-2-storage"}'/>
    <qemu:arg value='-device'/>
    <qemu:arg value='{"driver":"virtio-blk-pci","bus":"pci.7","addr":"0x0","drive":"libvirt-2-format","id":"virtio-disk2"}'/>
  </qemu:commandline>
</domain>

2. Fio testing in the guest on the nvme data disk
Test for 5 times:
#!/bin/bash

for i in 1 2 3 4 5 
do
    fio --rw=randrw --bs=4k --iodepth=8 --runtime=30 --ramp_time=5 --direct=1 --filename=/dev/vdb --name=job1 --ioengine=libaio --thread --group_reporting --cpus_allowed=0-7 --cpus_allowed_policy=split --numjobs=8 --time_based --output=/tmp/fio_result_${i}
    sleep 60
    echo "$i time fio is over."
done

Result:
Avg(Remove the highest and lowest values, then calculate the average):
Read: IOPS=129k
Write: IOPS=129k

1st time:
Read: IOPS=87.6k
Write: IOPS=87.6k

2nd time:
Read: IOPS=120k
Write: IOPS=120k

3rd time:
Read: IOPS=137k
Write: IOPS=137k

4th time:
Read: IOPS=130k
Write: IOPS=130k

5th time:
Read: IOPS=146k
Write: IOPS=146k

With 1 iothread:
Steps with the disk arg as below, others are the same as baseline:
.....
<qemu:arg value='{"driver":"virtio-blk-pci","bus":"pci.7","addr":"0x0","drive":"libvirt-2-format","id":"virtio-disk2","iothread": "iothread1"}'/>
….
   

Result:
Avg(Remove the highest and lowest values, then calculate the average):
Read: IOPS=85.4k
Write: IOPS=85.5k

1st time:
Read: IOPS=83.9k
Write: IOPS=84.0k

2nd time:
Read: IOPS=85.6k
Write: IOPS=85.6k

3rd time:
Read: IOPS=86.1k
Write: IOPS=86.1k

4th time:
Read: IOPS=84.7k
Write: IOPS=84.8k

5th time:
Read: IOPS=86.0k
Write: IOPS=86.1k

Expected results
The performance with the iothread is better than without

Actual results
The disk performance with an IOthread is worse than without any IOthreads.
Read(IOPS):85.4k vs 129k.