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RE: [Xen-devel] [PATCH] Fix hvm time issue.

>> >Do RTC and HPET need to be included as periodic timers? They are
>> used
>> >by Linux for ticks (it always uses PIT for jiffy updates) and I
>> >Windows is more robust against (or at least doesn't noticeably
>> >about) time jumps.
>> >
>> For RTC, yes! As we know some version of Windows uses RTC as main
>> resource for timekeeping.
>I suspect that it only does this because during boot it decides that it
>doesn't like the look of our pm_timer (I don't blame it!)
>It would be good to invest some effort understanding why it selects RTC
>-- I'm sure that it's a fall back.

I am not sure whether RTC is a fall back choice or not. The below
paragraph is from a paper of timekeeping in VMware. From the text, it
seems the answer is no. 

The timer device used and the number of interrupts generated per second
vary depending on which specific version of Microsoft Windows, and which
Windows HAL (hardware architecture layer), is installed. Most
uniprocessor Windows installations use the PIT as their main system
timer, but multiprocessor HALs and some ACPI uniprocessor HALs use the
CMOS periodic timer instead. For systems using the PIT, the base
interrupt rate is usually 100Hz, although Windows 98 uses 200Hz. For
systems that use the CMOS timer, the base interrupt rate is usually


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