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Re: [Xen-devel] Guest time and TSCs since changeset 17716

  • To: Frank Van Der Linden <Frank.Vanderlinden@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Mon, 29 Dec 2008 17:35:45 +0000
  • Cc:
  • Delivery-date: Mon, 29 Dec 2008 09:36:13 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Aclp2+D5hnsH4hHiEEqXlhtufqz2xw==
  • Thread-topic: [Xen-devel] Guest time and TSCs since changeset 17716

On 29/12/2008 17:23, "Frank Van Der Linden" <Frank.Vanderlinden@xxxxxxx>

> Changeset 17716 provides monotonically increasing guest time for HVM
> domains, by using the per-domain pl_time structure. hvm_get_guest_time
> and hvm_set_guest_time were changed to use this. Previously, the guest
> time was stored directly in the TSC offset fields of the vmx/smv control
> structures.
> Since pt_freeze_time and pt_thaw_time use hvm_get/set_guest_time, they
> now no longer freeze TSC time for a guest. So, for timer_mode 0, TSC
> time is no longer frozen when a VCPU is not running. Unless you're using
> opt_softtsc, in which TSC exactly tracks the per-domain values.
> I have no love for timer_mode 0 (it has serious issues on SMP), but was
> this change intentional? Or am I perhaps missing something?

It sounds unintentional, but as you say no one really uses timer_mode 0 so I
suppose it's gone unnoticed so far.

 -- Keir

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