[Xen-devel] Question on xen system time

["Yu, Ke" <ke.yu@xxxxxxxxx>]

In Xen x86 system time implementation (xen/arch/x86/time.c), there are
Per-CPU local system times and one global platform system time. local
system time is calibrated by TSC, and platform system time is calibrated
by platform timer (PIT/HPET/cyclone). 

My question is: is it possible not using TSC to calibrate local system
time, or even not using local system time, and using platform system
time instead? the rationale here is that: TSC is not reliable in some
cases. For example, in some old CPU, TSC frequency will change when CPU
frequency changes (in low power P state). TSC will even stop when CPU
enter deep C state. Linux actually choose not using TSC when CPU enter
deeper C state. I just wonder if it is possible in Xen. 

Best Regards
Yu Ke

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