On 12/15/2010 10:16 AM, Julien Desfossez wrote:
Hi,
I'm currently working with the kvm clocksource and I'm wondering if we
could implement the vread function for this clock source when we are
running on a host with constant_tsc.
If I understand correctly the hv_clock structure is per_cpu because of
the eventual frequency changes, but in the case of constant_tsc (and
after validation that the TSC is synchronized across all the cores) I
think we could have a working vread function.
In case of migration, could we have a fallback in case we detect we
end up on a CPU without constant_tsc ?
Any advice/explanation would be greatly appreciated !
It's a bit more complex than that. In addition to the problem you
mention with migration, even if the TSC is synchronized, the kvmclock
still is not, even with constant_tsc. There is measurement error in
between reading the TSC and computing the per_cpu hv_clock offset which
varies between CPUs.
Zach
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