Il 23/05/2013 15:20, Peter Lieven ha scritto: > On 23.05.2013 15:18, Paolo Bonzini wrote: >> Il 23/05/2013 14:25, Vadim Rozenfeld ha scritto: >>> >>> >>> ----- Original Message ----- >>> From: "Peter Lieven" <pl@xxxxxxxxx> >>> To: "Paolo Bonzini" <pbonzini@xxxxxxxxxx> >>> Cc: "Vadim Rozenfeld" <vrozenfe@xxxxxxxxxx>, "Marcelo Tosatti" >>> <mtosatti@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, gleb@xxxxxxxxxx, pl@xxxxxxx >>> Sent: Thursday, May 23, 2013 4:17:57 PM >>> Subject: Re: [RFC PATCH v2 1/2] add support for Hyper-V reference >>> time counter >>> >>> On 22.05.2013 23:55, Paolo Bonzini wrote: >>>> Il 22/05/2013 09:32, Vadim Rozenfeld ha scritto: >>>>>>> @@ -1827,6 +1829,29 @@ static int set_msr_hyperv_pw(struct >>>>>>> kvm_vcpu *vcpu, u32 msr, u64 data) >>>>>>> if (__copy_to_user((void __user *)addr, instructions, 4)) >>>>>>> return 1; >>>>>>> kvm->arch.hv_hypercall = data; >>>>>>> + local_irq_disable(); >>>>>>> + kvm->arch.hv_ref_count = get_kernel_ns(); >>>>>>> + local_irq_enable(); >>>>>>> + break; >>>>> local_irq_disable/local_irq_enable not needed. >>>>> >>>>> >>>>> What is the reasoning behind reading this time value at msr write >>>>> time? >>>>> [VR] Windows writs this MSR only once, during HAL initialization. >>>>> So, I decided to treat this call as a partition crate event. >>>>> >>>> >>>> But is it expected by Windows that the reference count starts counting >>>> up from 0 at partition creation time? If you could just use >>>> (get_kernel_ns() + kvm->arch.kvmclock_offset) / 100, it would also be >>>> simpler for migration purposes. >>> >>> I can just report, that I have used the patch that does it that way >>> and it works. >>> Maybe Windows is calculating the uptime by the reference counter? >>> >>> [VR] >>> Windows use it (reference counters/iTSC/PMTimer/HPET) as a time-stamp >>> source >>> for (Ke)QueryPerformanceCounter function. >> >> So I would prefer to remove kvm->arch.hv_ref_count altogether. > > But only if the migration support is guaranteed. Migration support wouldn't work yet anyway, you need to recompute the scale and sequence. But that could be done by KVM_SET_CLOCK. > And what if we have a host which lacks invariant TSC support? Then the sequence must be set to 0 or 0xFFFFFFFF, I still haven't understood. :) Paolo -- 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
