Re: [Xen-users] Getting synchronized time between domains on x86

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

El 10/08/15 a les 19.11, Jintack Lim ha escrit:
> Hi,
> 
> Is there any (easy) way to get synchronized time between domains(PV
> and HVM) on different physical cores on x86?
> On ARM architecture, reading CNTPCT_EL0 register gave me synchronous
> time across different physical cpu.
> 
> On x86, I have two domains, one is Dom0(PV), and the other is DomU(HVM).
> They are running on different set of cores, and I'd like to get
> synchronous time between them.
> I just read tsc register by calling rdtscll(), but it was not
> synchronized between them.

That's right, there's no guarantee that the TSC is synchronized between
CPU cores[0]. AFAICT this will only work if your hardware has an
invariant TSC[1] and tsc_mode is set to 2 for the HVM domain in the
configuration file.

Roger.

[0] https://en.wikipedia.org/wiki/Time_Stamp_Counter
[1] http://xenbits.xen.org/docs/unstable/misc/tscmode.txt

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