Re: [Xen-devel] common time reference between domU and dom0

[Keir Fraser <keir@xxxxxxx>]

On 10/12/2010 10:20, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

>> On 10/12/2010 08:23, "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
> wrote:
>> 
>>>> 
>>>> System time, as exposed to guests by Xen, should be good enough.
>>>> 
>>> 
>>> How is this exposed for HVM systems?
>> 
>> Given all HVM guest time sources are trapped to the hypervisor,
> including
>> TSC, you may as well just use the HVMOP_get_time hypercall.
>> 
> 
> Is that a new call? I don't see it mentioned in 4.0-testing anywhere.

Yeah I think it's in 4.1 only.

> Is there a fallback if HVMOP_get_time doesn't exist?

Switch on vtsc (might be default) and just use RDTSC? Might be good enough.
I'm not sure that computing system time yourself from fields in shared info
works well for HVM guests. HVMOP_get_time I think had been in XenServer
patch queue a while and has just been pulled across to upstream.

 -- Keir

> James
> 



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