On Tue, 2008-05-06 at 20:49 -0700, Zachary Amsden wrote: > > I suspect one of the problems is that there are too many state transitions > > to have it implemented with a low overhead on anything but S390, and even > > there you need milicoded instructions to handle things. > > > > If the number of transitions can be reduced, page hinting could be useful > > for KVM, too. > > Spot on Rik, if every transition becomes a hypercall (and a synchronous > one at that), it isn't workable for us. If, on the other hand, you > share the state bits between the guest and hypervisor, you need a giant > (standalone) bit array for per-page state, which is neither convenient > for Linux nor the hypervisor. I believe s390 has an 'instruction' to > migrate the state bits into the hypervisor per-physical-page data > without requiring a hypercall. That is why we invented the millicoded ESSA instruction on s390. We had an emulation of the instruction to test things. It worked but was awfully slow. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
