Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC

[Gleb Natapov <gleb@redhat.com>]

On Thu, May 23, 2013 at 10:35:59AM -0300, Marcelo Tosatti wrote:
> 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.
Proper implementation will disable reference TSC in this case.

--
			Gleb.