[Xen-devel] swiotlb=force in Konrad's xen-pcifront-0.8.2 pvops domU kernel with PCI passthrough

[Dante Cinco <dantecinco@xxxxxxxxx>]

We have Fibre Channel HBA devices that we PCI passthrough to our pvops
domU kernel. Without swiotlb=force in the domU's kernel command line,
both domU and dom0 lock up after loading the kernel module drivers for
the HBA devices. With swiotlb=force, the domU and dom0 are stable
after loading the kernel module drivers but the I/O performance is at
least an order of magnitude worse than what we were seeing with the
HVM kernel. I see the following in /var/log/kern.log in the pvops
domU:

PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
Placing 64MB software IO TLB between ffff880005800000 - ffff880009800000
software IO TLB at phys 0x5800000 - 0x9800000

Is swiotlb=force responsible for the I/O performance degradation? I
don't understand what swiotlb=force does so I would appreciate an
explanation or a pointer.

Thanks.

- Dante

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel