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.
And what if we have a host which lacks invariant TSC support?
Peter
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
