<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Best explanation I’ve found is <a href="https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-data-plane.29" class="">https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-data-plane.29</a> If you google a bit, you’ll find some more under QEMU topics, I saw some discussion of threads and queues in virtio-scsi, but that seems to be a slightly different thing than this setting.<div class=""><br class=""></div><div class="">In short, having at least 1 offers advantages for all your VM’s disks, and if you want to be optimal (at the possible expense of extra CPU for IO), one per drive attached. There is (currently) no benefit to having more than 1 thread per drive. From what I can tell, if you have more drives than threads they share the threads evenly and are statically assigned to a thread. Seems to be effective at QEMU start, so you have to change it with the VM down or stop and start it again.</div><div class=""><br class=""></div><div class="">I currently enable it on all VMs and assign 1 thread per drive on my systems.<br class=""><div><blockquote type="cite" class=""><hr style="border:none;border-top:solid #B5C4DF 1.0pt;padding:0 0 0 0;margin:10px 0 5px 0;" class=""><span style="margin: -1.3px 0.0px 0.0px 0.0px" id="RwhHeaderAttributes" class=""><font face="Helvetica" size="4" color="#000000" style="font: 13.0px Helvetica; color: #000000" class=""><b class="">From:</b> Gianluca Cecchi <<a href="mailto:gianluca.cecchi@gmail.com" class="">gianluca.cecchi@gmail.com</a>></font></span><br class="">
<span style="margin: -1.3px 0.0px 0.0px 0.0px" class=""><font face="Helvetica" size="4" color="#000000" style="font: 13.0px Helvetica; color: #000000" class=""><b class="">Subject:</b> [ovirt-users] VM resource allocation and IO Threads</font></span><br class="">
<span style="margin: -1.3px 0.0px 0.0px 0.0px" class=""><font face="Helvetica" size="4" color="#000000" style="font: 13.0px Helvetica; color: #000000" class=""><b class="">Date:</b> October 27, 2017 at 9:26:59 AM CDT</font></span><br class="">
<span style="margin: -1.3px 0.0px 0.0px 0.0px" class=""><font face="Helvetica" size="4" color="#000000" style="font: 13.0px Helvetica; color: #000000" class=""><b class="">To:</b> users</font></span><br class="">
<br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hello,<div class="">can anyone give any pointer to deeper information about what in subject and the value for "Num Of IO Threads" configuration, best practices and to-be-expected improvements?</div><div class=""><br class=""></div><div class="">I read also here:</div><div class=""><a href="https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html-single/virtual_machine_management_guide/#Editing_IO_Threads" class="">https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html-single/virtual_machine_management_guide/#Editing_IO_Threads</a><br class=""></div><div class=""><br class=""></div><div class="">but in some points it seems not so clear to me:</div><div class=""><br class=""></div><div class="">eg:</div><div class=""><br class=""></div><div class=""><div class="">If a virtual machine has more than one disk, you can enable or change the number of IO threads to improve performance.</div></div><div class=""><br class=""></div><div class="">but also</div><div class=""><br class=""></div><div class=""><div class="">Red Hat recommends using the default number of IO threads, which is 1.</div></div><div class=""><br class=""></div><div class="">There is also a note about deactivation and activation of disks: does it mean that even if I poweroff the VM and change its config I have to make this step after?</div><div class=""><br class=""></div><div class="">Anyone has run benchmarks?</div><div class="">Does it make sense if my VM has 3 disks to configure 6 IO threads for example?</div><div class="">Do IO threads map to SCSI controllers inside the guest or what?</div><div class=""><br class=""></div><div class="">Thanks in advance,<br class=""></div><div class="">Gianluca</div></div>
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