Re: [Xen-devel] [PATCH v2 8/9] x86/intel_pstate: support the use of intel_pstate in pmstat.c

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

On 05/06/2015 15:22, Jan Beulich wrote
> >>> "Wang, Wei W" <wei.w.wang@xxxxxxxxx> 06/04/15 4:21 AM >>>
> >On 26/05/2015 22:16, Jan Beulich wrote
> >> >>> On 13.05.16 at 09:51, <wei.w.wang@xxxxxxxxx> wrote:
> >> > --- a/xen/drivers/acpi/pmstat.c
> >> > +++ b/xen/drivers/acpi/pmstat.c
> >> > @@ -261,29 +272,47 @@ static int get_cpufreq_para(struct
> >> xen_sysctl_pm_op *op)
> >> >      op->u.get_para.cpuinfo_max_freq = policy->cpuinfo.max_freq;
> >> >      op->u.get_para.cpuinfo_min_freq = policy->cpuinfo.min_freq;
> >> >      op->u.get_para.scaling_cur_freq = policy->cur;
> >> > -    op->u.get_para.scaling_max_freq = policy->max;
> >> > -    op->u.get_para.scaling_min_freq = policy->min;
> >> > +    if (policy->policy) {
> >> > +        op->u.get_para.scaling_max.max_perf_pct = policy-
> >max_perf_pct;
> >> > +        op->u.get_para.scaling_min.min_perf_pct = policy->min_perf_pct;
> >> > +        op->u.get_para.scaling_turbo_pct = policy->turbo_pct;
> >> > +    } else {
> >> > +        op->u.get_para.scaling_max.max_freq = policy->max;
> >> > +        op->u.get_para.scaling_min.min_freq = policy->min;
> >> > +    }
> >>
> >> How does the caller then know which of the union member meanings
> >> apply?
> >
> >The end caller is xenpm. It's aware of the running pstate driver, so it
> >knows  the difference between freq and pct.
> 
> xenpm is one of the possible callers. We don't make hypercalls with just a
> single consumer in mind, excluding any other potential one(s). And hence a
> hypercall like this should be kind of self contained, i.e. in the case here 
> the
> caller ought to be able to know from its result which of the union fields are 
> in
> use.

Ok. It's actually already self-contained. The "scaling_driver" field indicates 
which union filed the caller should use. This is also how xenpm uses it.

Best,
Wei

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