Re: [Xen-devel] [PATCH] x86/time: update TSC stamp on restore from deep C-state

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.01.2020 20:36, Igor Druzhinin wrote:
> If ITSC is not available on CPU (e.g if running nested as PV shim)
> then X86_FEATURE_NONSTOP_TSC is not advertised in certain cases, i.e.
> all AMD and some old Intel processors. In which case TSC would need to
> be restored on CPU from platform time by Xen upon exiting deep C-states.

How does waking from deep C states correspond to the PV shim? I notice
that cstate_restore_tsc() gets called irrespective of the C state being
exited, so I wonder whether there's room for improvement there
independent of the issue at hand. As far as this change is concerned,
I think you want to drop the notion of "deep" from the description.

Jan

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