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

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

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.

Hi Jan,

Please have a check my conclusion of the changes. 
By the way, just a reminder for people who were not involved in the discussion 
before: the changed things in this patchset are intel_pstate specific. The 
changes in xenpm only take effect when the intel_pstate driver is loaded. If 
"intel_pstate=enable" is not added to the booting parameter list, all the 
things will work in their old style as before.

NO.1
The intel_pstate driver can be controlled via two ways:
1) min_perf_pct and max_perf_pct
The user directly adjusts min_perf_pct and max_perf_pct to get what they want. 
For example, if min_perf_pct=max_perf_pct=60%, then the user is asking for 
something similar to a userspace governor with setting the requested 
performance=60%.
2) set-scaling-governor
This one is functionally redundant, since 1) can achieve all the governor 
functions. It is remained to give people time to get familiar with method 1).
Users can choose from the four governors: Powersave, Ondemand, Powersave, 
Performance.
The driver will achieve the functionality of the selected governor via 
adjusting the min_perf_pct and max_perf_pct itself.

NO.2
The xenpm "get-cpufreq-para" will display the following things:
cpu id                            : 0
affected_cpus           : 0
cpuinfo frequency   : max [3700000] min [1200000] cur [1200000]
scaling_driver            : intel_pstate
scaling_avail_gov     : Performance Powersave Ondemand Userspace
current_governor    : Ondemand
max_perf_pct           : 100
min_perf_pct            : 32
turbo_pct                    : 54
turbo mode                : enabled

The governor info (scaling_avail_gov and current_governor) is still remained 
here, because there is no "get-scaling-governor" interface in xenpm. In the 
future when we remove "set-scaling-governor", we can remove the two lines.
Also, the pstate_num line, which shows the total number of the CPU's P-states, 
is removed.


NO.3
Change "intel_pstate=disable" with "intel_pstate=enable" to specifically 
request the loading of the intel_pstate driver.

NO.4
We will move the declarations under xen/include/acpi to an x86-specific header.

Best,
Wei

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