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

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 15/01/2020 11:32, Jan Beulich wrote:
> 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.

I'm not familiar with what to call "deep C-state" so for me it was anything
higher than C1. If you prefer "deep" to be dropped - so be it.

Igor

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel