On Thu, May 12, 2011 at 05:37:43PM +0300, Avi Kivity wrote: > On 05/12/2011 05:24 PM, Joerg Roedel wrote: > One thing we could do is paravirtualize at a lower level, introduce a > hypercall for batch MSR reads and writes. So we can use the existing > PMU semantics and code, just optimize the switch. This is similar to > what Xen did with lazy cpu updates, and what kvm did for paravirt > pagetable writes. In general a good idea. For MSR writes this isn't trivial as well. MSR reads and writes can cause a #GP, this needs to be represented in this interface. Can we allow that a batched MSR write changes the operation mode of the vcpu and so on. Or we limit this interface to the PMU MSRs, then we are pretty much at a paravirt-pmu. > I've considered something similar for mmio - use hypercalls for ordinary > mmio to avoid calling into the emulator - but virtio uses pio which > isn't emulated and we don't have massive consumers of mmio (except > perhaps hpet). > > (and we can have a cpuid bit that advertises whether we recommend to use > this feature for PMU MSRs; if/when we get hardware support, we turn it > off) A cpuid-bit that indicates which pmu is prefered is certainly a good idea. Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
