RE: [Xen-ia64-devel] Question about migration

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

> 
>   The kernel guarantees applications only see time move forward, even
> across multiple CPUs.  See: 
> 
> kernel/timer.c:time_interpolator_get_counter()
> 
> We never return a time before last_cycle unless booted with the
> "nojitter" options. 
> 

Echo from me too.
I was told some time ago, the crystal used in IPF platform is usually
expansive
than other platforms and thus much more accurate.
Normally the small difference won;t cause application see backward ITC
value,
but live migration per current Xen time virtualization policy is another
story. It
could be a headache :(

Hopefully some time later, with Tukwila, we can live with hybrid
virtualization, 
thus we got the problem solved by HW trapping application ITC read :)
Or if some platform has high resolution platform time, we can restore
physical ITC
at VP switch time. (platform_time + per VP offset)

Eddie

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