Re: [Xen-devel] #599161: Xen debug patch for the "clock shifts by 50 minutes" bug.

[Keir Fraser <keir@xxxxxxx>]

On 08/11/2012 14:28, "Ian Campbell" <ijc@xxxxxxxxxxxxxx> wrote:

>>> There appears to be a certain amount of hardware-specificness to the
>>> issue -- so I'm wondering if maybe there are some platforms whose tsc is
>>> not as monotonically increasing as it needs to be...
>> 
>> plt_* timestamps are not derived from TSC at all.
> 
> I see, rather it is derived from the platform_timesource which could be
> HPET, pmtimer, pit etc but in this case (according to the provided xm
> dmesg) appears to be a 14MHz HPET.
> 
> So I guess s/tsc/HPET/ in my original thought...

In fact plt_now and plt_wrap are both derived from the same value of
plt_stamp64. One is derived from it directly, and the other from
plt_stamp64+plt_mask+1 (== plt_stamp64+(1<<32)).

 -- Keir



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