[ovirt-devel] 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
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