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xen-devel
RE: [Xen-devel] xen tsc problems?
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>
> On 13/07/2010 15:37, "Stefano Stabellini"
> <Stefano.Stabellini@xxxxxxxxxxxxx>
> wrote:
>
> > Does this mean that the host has some serious tsc issues?
> > Can this be a symptom of a bug in xen?
> > Suggestion are welcome.
>
> The 's' and 't' debug key handlers will be useful to get an idea of how
> stable host TSCs are.
>
> -- Keir
Also you can try max_cstate=0 as a Xen boot parameter to rule
out power management screwing up the tsc.
> > Does this mean that the host has some serious tsc issues?
Probably. But the default tsc_mode (0) is intended to hide all
such issues. Could you check the 's' debug-key output to
ensure your guest is actually running with tsc_mode=0?
> > Can this be a symptom of a bug in xen?
Well, if the guest has problems with the default tsc_mode (0),
which does complete tsc emulation, I suppose it could be
a bug in Xen. In particular, I wonder if the code that
recovers from deep C-states (and writes to the TSC) is broken.
IIRC, there was some changesets in that area recently.
If the problem goes away with max_cstate=0, that would be
a good place to start.
Dan
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