On Tue, Aug 21, 2007 at 10:23:14PM -0700, Zachary Amsden wrote: > In general, I/O in a virtual guest is subject to performance problems. > The I/O can not be completed physically, but must be virtualized. This > means trapping and decoding port I/O instructions from the guest OS. > Not only is the trap for a #GP heavyweight, both in the processor and > the hypervisor (which usually has a complex #GP path), but this forces > the hypervisor to decode the individual instruction which has faulted. Is that really that expensive? Hard to imagine. e.g. you could always have a fast check for inb/outb at the beginning of the #GP handler. And is your initial #GP entry really more expensive than a hypercall? > Worse, even with hardware assist such as VT, the exit reason alone is > not sufficient to determine the true nature of the faulting instruction, > requiring a complex and costly instruction decode and simulation. It's unclear to me why that should be that costly. Worst case it's a switch() -Andi _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
