From: Gianluca Cecchi <gianluca.cecchi@gmail.com> Subject: [ovirt-users] VM resource allocation and IO Threads Date: October 27, 2017 at 9:26:59 AM CDT To: users =20 Hello, can anyone give any pointer to deeper information about what in = subject and the value for "Num Of IO Threads" configuration, best =
=20 I read also here: = https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/h= tml-single/virtual_machine_management_guide/#Editing_IO_Threads = <https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/=
=20 but in some points it seems not so clear to me: =20 eg: =20 If a virtual machine has more than one disk, you can enable or change =
--Apple-Mail=_D4C1048E-6102-423F-8DB0-C4D43E76E17F Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Best explanation I=E2=80=99ve found is = https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-data-plane.2= 9 If you google a bit, you=E2=80=99ll 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. In short, having at least 1 offers advantages for all your VM=E2=80=99s = 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. =46rom 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. I currently enable it on all VMs and assign 1 thread per drive on my = systems. practices and to-be-expected improvements? html-single/virtual_machine_management_guide/#Editing_IO_Threads> the number of IO threads to improve performance.
=20 but also =20 Red Hat recommends using the default number of IO threads, which is 1. =20 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? =20 Anyone has run benchmarks? Does it make sense if my VM has 3 disks to configure 6 IO threads for = example? Do IO threads map to SCSI controllers inside the guest or what? =20 Thanks in advance, Gianluca _______________________________________________ Users mailing list Users@ovirt.org http://lists.ovirt.org/mailman/listinfo/users
--Apple-Mail=_D4C1048E-6102-423F-8DB0-C4D43E76E17F Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8 <html><head><meta http-equiv=3D"Content-Type" content=3D"text/html; = charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; = -webkit-nbsp-mode: space; line-break: after-white-space;" class=3D"">Best = explanation I=E2=80=99ve found is <a = href=3D"https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-data= -plane.29" = class=3D"">https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-d= ata-plane.29</a> If you google a bit, you=E2=80=99ll 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=3D""><br class=3D""></div><div class=3D"">In short, = having at least 1 offers advantages for all your VM=E2=80=99s 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. =46rom 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=3D""><br = class=3D""></div><div class=3D"">I currently enable it on all VMs and = assign 1 thread per drive on my systems.<br class=3D""><div><blockquote = type=3D"cite" class=3D""><hr style=3D"border:none;border-top:solid = #B5C4DF 1.0pt;padding:0 0 0 0;margin:10px 0 5px 0;" class=3D""><span = style=3D"margin: -1.3px 0.0px 0.0px 0.0px" id=3D"RwhHeaderAttributes" = class=3D""><font face=3D"Helvetica" size=3D"4" color=3D"#000000" = style=3D"font: 13.0px Helvetica; color: #000000" class=3D""><b = class=3D"">From:</b> Gianluca Cecchi <<a = href=3D"mailto:gianluca.cecchi@gmail.com" = class=3D"">gianluca.cecchi@gmail.com</a>></font></span><br class=3D""> <span style=3D"margin: -1.3px 0.0px 0.0px 0.0px" class=3D""><font = face=3D"Helvetica" size=3D"4" color=3D"#000000" style=3D"font: 13.0px = Helvetica; color: #000000" class=3D""><b class=3D"">Subject:</b> = [ovirt-users] VM resource allocation and IO Threads</font></span><br = class=3D""> <span style=3D"margin: -1.3px 0.0px 0.0px 0.0px" class=3D""><font = face=3D"Helvetica" size=3D"4" color=3D"#000000" style=3D"font: 13.0px = Helvetica; color: #000000" class=3D""><b class=3D"">Date:</b> October = 27, 2017 at 9:26:59 AM CDT</font></span><br class=3D""> <span style=3D"margin: -1.3px 0.0px 0.0px 0.0px" class=3D""><font = face=3D"Helvetica" size=3D"4" color=3D"#000000" style=3D"font: 13.0px = Helvetica; color: #000000" class=3D""><b class=3D"">To:</b> = users</font></span><br class=3D""> <br class=3D"Apple-interchange-newline"><div class=3D""><div dir=3D"ltr" = class=3D"">Hello,<div class=3D"">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=3D""><br class=3D""></div><div class=3D"">I read also = here:</div><div class=3D""><a = href=3D"https://access.redhat.com/documentation/en-us/red_hat_virtualizati= on/4.1/html-single/virtual_machine_management_guide/#Editing_IO_Threads" = class=3D"">https://access.redhat.com/documentation/en-us/red_hat_virtualiz= ation/4.1/html-single/virtual_machine_management_guide/#Editing_IO_Threads= </a><br class=3D""></div><div class=3D""><br class=3D""></div><div = class=3D"">but in some points it seems not so clear to me:</div><div = class=3D""><br class=3D""></div><div class=3D"">eg:</div><div = class=3D""><br class=3D""></div><div class=3D""><div class=3D"">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=3D""><br class=3D""></div><div class=3D"">but also</div><div = class=3D""><br class=3D""></div><div class=3D""><div class=3D"">Red Hat = recommends using the default number of IO threads, which is = 1.</div></div><div class=3D""><br class=3D""></div><div class=3D"">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=3D""><br class=3D""></div><div = class=3D"">Anyone has run benchmarks?</div><div class=3D"">Does it make = sense if my VM has 3 disks to configure 6 IO threads for = example?</div><div class=3D"">Do IO threads map to SCSI controllers = inside the guest or what?</div><div class=3D""><br class=3D""></div><div = class=3D"">Thanks in advance,<br class=3D""></div><div = class=3D"">Gianluca</div></div> _______________________________________________<br class=3D"">Users = mailing list<br class=3D""><a href=3D"mailto:Users@ovirt.org" = class=3D"">Users@ovirt.org</a><br = class=3D"">http://lists.ovirt.org/mailman/listinfo/users<br = class=3D""></div></blockquote></div><br class=3D""></div></body></html>= --Apple-Mail=_D4C1048E-6102-423F-8DB0-C4D43E76E17F--