----- Original Message ----- From: "Marcelo Tosatti" <mtosatti@xxxxxxxxxx> To: "Gleb Natapov" <gleb@xxxxxxxxxx> Cc: "Peter Lieven" <pl@xxxxxxxxx>, "Vadim Rozenfeld" <vrozenfe@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, pl@xxxxxxx Sent: Thursday, May 23, 2013 11:35:59 PM Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC On Thu, May 23, 2013 at 12:13:16PM +0300, Gleb Natapov wrote: > > > > > >"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. > > > Reference TSC is even faster. There should be no crashed with proper > implementation. > > -- > Gleb. Lack of invariant TSC support in the host. if there is no iTSC in the host -> set sequence to 0 and go with reference counter. It is why they both scaled to 10 MHz, and it's why reference counters is a fall-back for iTSC. -- 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
