Re: Libvirt driver iothread property for virtio-scsi disks

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.

> 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 :|