----- Original Message ----- From: "Peter Lieven" <[email protected]> To: "Vadim Rozenfeld" <[email protected]> Cc: "Marcelo Tosatti" <[email protected]>, [email protected], [email protected], [email protected] Sent: Thursday, May 23, 2013 10:44:14 PM Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC
On 23.05.2013 14:33, Vadim Rozenfeld wrote: > > > ----- Original Message ----- > From: "Peter Lieven" <[email protected]> > To: "Marcelo Tosatti" <[email protected]> > Cc: "Vadim Rozenfeld" <[email protected]>, [email protected], > [email protected], [email protected] > Sent: Thursday, May 23, 2013 4:18:55 PM > Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC > > On 22.05.2013 23:23, Marcelo Tosatti wrote: >> On Wed, May 22, 2013 at 03:22:55AM -0400, Vadim Rozenfeld wrote: >>> >>> >>> ----- Original Message ----- >>> From: "Marcelo Tosatti" <[email protected]> >>> To: "Vadim Rozenfeld" <[email protected]> >>> Cc: [email protected], [email protected], [email protected] >>> Sent: Wednesday, May 22, 2013 10:50:46 AM >>> Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC >>> >>> On Sun, May 19, 2013 at 05:06:37PM +1000, Vadim Rozenfeld wrote: >>>> The following patch allows to activate a partition reference >>>> time enlightenment that is based on the host platform's support >>>> for an Invariant Time Stamp Counter (iTSC). >>>> NOTE: This code will survive migration due to lack of VM stop/resume >>>> handlers, when offset, scale and sequence should be >>>> readjusted. >>>> >>>> --- >>>> arch/x86/kvm/x86.c | 6 +++++- >>>> 1 file changed, 5 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index 9645dab..b423fe4 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -1838,7 +1838,6 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, >>>> u32 msr, u64 data) >>>> u64 gfn; >>>> unsigned long addr; >>>> HV_REFERENCE_TSC_PAGE tsc_ref; >>>> - tsc_ref.TscSequence = 0; >>>> if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE)) { >>>> kvm->arch.hv_tsc_page = data; >>>> break; >>>> @@ -1848,6 +1847,11 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, >>>> u32 msr, u64 data) >>>> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT); >>>> if (kvm_is_error_hva(addr)) >>>> return 1; >>>> + tsc_ref.TscSequence = >>>> + boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? 1 : 0; >>> >>> 1) You want NONSTOP_TSC (see 40fb1715 commit) which matches INVARIANT TSC. >>> [VR] >>> Thank you for reviewing. Will fix it. >>> 2) TscSequence should increase? >>> "This field serves as a sequence number that is incremented whenever..." >>> [VR] >>> Yes, on every VM resume, including migration. After migration we also need >>> to recalculate scale and adjust offset. >>> 3) 0xFFFFFFFF is the value for invalid source of reference time? >>> [VR] Yes, on boot-up. In this case guest will go with PMTimer (not sure >>> about HPET >>> but I can check). But if we set sequence to 0xFFFFFFFF after migration - >>> it's probably will not work. >> >> "Reference TSC during Save and Restore and Migration >> >> To address migration scenarios to physical platforms that do not support >> iTSC, the TscSequence field is used. In the event that a guest partition >> is migrated from an iTSC capable host to a non-iTSC capable host, the >> hypervisor sets TscSequence to the special value of 0xFFFFFFFF, which >> directs the guest operating system to fall back to a different clock >> source (for example, the virtual PM timer)." >> >> Why it would not/does not work after migration? >> >> > > what exactly do we heed the reference TSC for? the reference counter alone > works great and it seems > that there is a lot of trouble and crash possibilities involved with the > referece tsc. > > [VR] > Because it is incredibly light and fast. > The simple test which calls QueryPerformanceCounter in a > loop 10 millions times gives we the following results: > PMTimer 32269 ms > HPET 38466 ms > Ref Count 6499 ms > iTSC 1169 ms is the ref_count with local_irq_disable or preempt_disable? [VR] local_irq_disable Peter -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
