[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/time: update TSC stamp on restore from deep C-state
On 15.01.2020 13:28, Igor Druzhinin wrote: > 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. "Higher than C1" may be fine (albeit I vaguely recall TSC issues starting with C3 only), but at least mwait_idle() calls the function even for C1. As to the PV shim - does it know about any C-states at all (beyond HLT-invoked C1)? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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