As stated previously, 1 IO thread is somewhat sane choice. Multiple IO threads make sense if you have multiple storage devices across different NUMA nodes.
mpolednik On Mon, Oct 30, 2017 at 4:29 PM, Darrell Budic <[email protected]> wrote: > Best explanation I’ve found is > https://wiki.mikejung.biz/KVM_/_Xen#virtio-blk_iothreads_.28x-data-plane.29 > 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. > > 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. > > I currently enable it on all VMs and assign 1 thread per drive on my > systems. > > ________________________________ > From: Gianluca Cecchi <[email protected]> > Subject: [ovirt-users] VM resource allocation and IO Threads > Date: October 27, 2017 at 9:26:59 AM CDT > To: users > > Hello, > 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? > > I read also here: > https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html-single/virtual_machine_management_guide/#Editing_IO_Threads > > but in some points it seems not so clear to me: > > eg: > > If a virtual machine has more than one disk, you can enable or change the > number of IO threads to improve performance. > > but also > > Red Hat recommends using the default number of IO threads, which is 1. > > 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? > > 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? > > Thanks in advance, > Gianluca > _______________________________________________ > Users mailing list > [email protected] > http://lists.ovirt.org/mailman/listinfo/users > > > > _______________________________________________ > Users mailing list > [email protected] > http://lists.ovirt.org/mailman/listinfo/users > _______________________________________________ Users mailing list [email protected] http://lists.ovirt.org/mailman/listinfo/users
