Re: [Xen-devel] [PATCH 0/9] Porting the intel_pstate driver to Xen

["Wang, Wei W" <wei.w.wang@xxxxxxxxx>]

On 29/04/2015 07:10, Jan Beulich wrote
> >>> "Wang, Wei W" <wei.w.wang@xxxxxxxxx> 04/28/15 4:38 PM >>>
> >On 28/04/2015 21:29, Jan Beulich wrote
> >>>>> "Wang, Wei W" <wei.w.wang@xxxxxxxxx> 04/28/15 3:24 PM >>>
> >> >On 28/04/2015 21:14, Jan Beulich wrote
> >> >>  >On 25/04/2015 00:15, Konrad Rzeszutek Wilk wrote
> >> >> >> How will this affect AMD processors which can use the cpufreq?
> >> >> >> Would the ondemand feature go away?
> >> >> >
> >> >> >No, this won't affect them. When the "intel_pstate=disable" is
> >> >> >added to the  booting parameter list, the old cpufreq driver will
> >> >> >be used, and everything,  including xenpm, will work in the old style.
> >> >>
> >> >> That wouldn't suffice. On AMD (and older Intel) platforms it
> >> >> shouldn't be necessary to specifiy the option to retain current
> >> functionality.
> >> >
> >> >No problem, I will change it with "intel_pstate=enable" to enable
> >> >the intel_pstate driver. Then others will not be bothered.
> >>
> >> For new code this might be a good idea anyway, but that wasn't my point.
> >> Instead, even with "intel_pstate=enable" on an old Intel (or AMD)
> >> system (regardless of doing so being pointless) there shouldn't be
> >> any behavioral difference.
> >
> >Without " intel_pstate=enable" added, the old acpi-cpufreq driver will be
> loaded, so shouldn't be a problem.
> 
> While I would have thought this to be an obvious thing anyway, it looks like
> we still don't understand each other. As much as it is (supposed to be)
> natural that in the absence of that command line option things behave as
> before, it should also be so if the option _was_ given but the driver didn't
> find suitable hardware.

The intel_pstate driver will check if the running CPU is included in the table 
which contains all the supported CPUs. If not, we can unregister the 
intel_pstate driver and have the old one loaded.

Best,
Wei


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