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

  • To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>
  • Date: Wed, 6 Dec 2006 17:12:29 +0800
  • Delivery-date: Wed, 06 Dec 2006 01:13:08 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AccY9ZdVfqpS/yfBQWi+K0GDJLORiQAHVK2EAAA7LpA=
  • Thread-topic: [Xen-devel] [PATCH] Fix hvm time issue.

>Do RTC and HPET need to be included as periodic timers? They are never
>by Linux for ticks (it always uses PIT for jiffy updates) and I think
>Windows is more robust against (or at least doesn't noticeably complain
>about) time jumps.

For RTC, yes! As we know some version of Windows uses RTC as main time
resource for timekeeping. We noticed if it's not added as periodic
timer, Windows time may go slow in SMP environment.
In case of HPET, the answer may be no, as OS can read the monotonically
increased counter to see time jumps.

And as periodic timer list is per vcpu, it's also helpful to sync one
vcpu's lapic time with its TSC, which is needed when guest calibrates
lapic at least.


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