On Wed, Nov 4, 2020 at 6:54 PM Daniel P. Berrangé <berrange@xxxxxxxxxx> wrote: > > On Wed, Nov 04, 2020 at 05:48:40PM +0200, Nir Soffer wrote: > > The docs[1] say: > > > > - The optional iothread attribute assigns the disk to an IOThread as defined by > > the range for the domain iothreads value. Multiple disks may be assigned to > > the same IOThread and are numbered from 1 to the domain iothreads value. > > Available for a disk device target configured to use "virtio" bus and "pci" > > or "ccw" address types. Since 1.2.8 (QEMU 2.1) > > > > Does it mean that virtio-scsi disks do not use iothreads? > > > > I'm experiencing a horrible performance using nested vms (up to 2 levels of > > nesting) when accessing NFS storage running on one of the VMs. The NFS > > server is using scsi disk. > > When you say 2 levels of nesting do you definitely have KVM enabled at > all levels, or are you ending up using TCG emulation, because the latter > would certainly explain terrible performance. Good point, I'll check that out, thanks. > > My theory is: > > - Writing to NFS server is very slow (too much nesting, slow disk) > > - Not using iothreads (because we don't use virtio?) > > - Guest CPU is blocked by slow I/O > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >