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Re: [Xen-devel] clock source in PV Linux

On 12/18/19 12:36 AM, Roman Shaposhnik wrote:
On Wed, Dec 11, 2019 at 12:41 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
On 11.12.2019 09:16, Jürgen Groß wrote:
On 11.12.19 08:28, Jan Beulich wrote:
Jürgen, Boris,

I've noticed

<6>clocksource: Switched to clocksource tsc

as the final clocksource related boot message in a PV Dom0's
log with 5.4.2. Is it intentional that it's not the "xen" one
that gets used by default?
I think this is fine. I just tested it and I'm seeing the same in dom0,
while in a PV domU "xen" is used per default.

In dom0 "tsc" should be okay in case it is stable. Or are you expecting
problems with that setting?
Well, first of all I found this surprising. Whether there are problems to
be expected largely depends on the reliability of the "stable" detection
in PV Dom0.
Related question: does this mean that tsc is now default for PVH as well?

The reason I'm asking is because I'm still a bit worried about the
clock drift with tsc.

dom0 will use TSC for either PV or PVH:

       /* As Dom0 is never moved, no penalty on using TSC there */
        if (xen_initial_domain())
                xen_clocksource.rating = 275;

But as far as TSC stability I'd think it should be sufficiently checked by generic TSC init code?


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