RE: [Xen-devel] Re: system freeze when processor.ko is loaded

["Wang, Winston L" <winston.l.wang@xxxxxxxxx>]

> >>> On 12.04.11 at 00:35, "Wang, Winston L" <winston.l.wang@xxxxxxxxx>
> wrote:
> > I think restore only the lower 32bit TSC is good enough, why do we
> need to touch upper 32 bit TSC?
> 
> You just can't: A wrmsr to this MSR always updates the full 64-bits,
> just that on some CPUs this update implies the upper 32 bits getting
> zeroed.
You are right, just can't only write lower 32 bit without updating 32 bit since 
TSC is always 64 bits:(
So we have to give up the deep C state for those old processors since we still 
need to maintain TSC all the time for SMP support.
The solution should go with your patch: re-validate the processor boot with " 
X86_FEATURE_TSC_RELIABLE" to see upper 32 bit TSC MSR is writeable at 
init_xen_time or not , then decide if allow deep_cstate. This is a better idea 
than only allow the processor going to the deep c state with 
"x86_FEATURE_CONSTANT_TSC but !X86_FEATURE_NONSTOP_TSC CPUs".

Would you double test patch before pulling in? we need to check both the old 
failed processor and the current one. And what's the power idle power impact.
> 
> And even if you could, it wouldn't be easy to deal with the situation
> where the update would carry into the upper 32 bits.
> 
> Jan
> 
> > 1. I would not think if any processor's deep c-state wakeup from idle
> can
> > more than 100 ms.
> > 2. For 3GHZ processor lower 32bit TSC wrapper around time is ~2.83
> Sec.
> > 3. The platform timer (22bit ACPI timer) wrapper around is 2.34 sec
> (this is
> > used for counting the delta before enter deep_cstate and before
> wakeup)
> > Just need to change cstate_restore_tsc() and only patch back the
> delta time
> > to the lower 32 bit TSC to make that simple?
> >
> > Winston,
> 
> 


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