Re: [PATCH 2/5] cpufreq/hwp: move driver data into policy

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2026-01-26 04:08, Jan Beulich wrote:
> On 23.01.2026 23:35, Jason Andryuk wrote:
> > On 2026-01-22 04:42, Jan Beulich wrote:
> > > Share space with the ACPI and powernow drivers, avoiding a separate
> > > allocation for each CPU. Except for get_hwp_para() all use sites already
> > > have the policy available, and this one function can simply be brought
> > > closer to its sibling set_hwp_para().
> > Minor, but maybe 's/function/function's signature/'.  The original
> > phrasing made me think it was code movement.
> I don't see an issue there, but I've adjusted as you asked for.
Thank you.

> > > This then also eliminates the concern over hwp_cpufreq_cpu_init() being
> > > called for all CPUs
> > We expect hwp_cpufreq_cpu_init() to be called for each CPU, so I am
> > confused by this statement.  The data...
> Well, "expect" is the problem. Recall my pointing out of the problem when
> having noticed the same pattern in the amd-cppc driver patches. My
> recollection from the discussion is that there's no formal statement of
> ...
>
> >   >, or a CPU going offline that's recorded in> policy->cpu (which would
> > result in accesses of per-CPU data of offline
> > > CPUs).
> > >
> > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > > ---
> > > hwp_cpufreq_target() still requires policy->cpu to be online, though.
> > >
> > > --- a/xen/arch/x86/acpi/cpufreq/hwp.c
> > > +++ b/xen/arch/x86/acpi/cpufreq/hwp.c
> > > -static DEFINE_PER_CPU_READ_MOSTLY(struct hwp_drv_data *, hwp_drv_data);
> > ... here is tracked and filled per-CPU.
> >
> > Do we need cpufreq_add_cpu() to force hw_all = 1 for HWP (and maybe
> > AMD-CPPC) to ensure that policy is allocated per-CPU?
> ... this being a correct thing to do, hence our code imo would better be
> resilient to it being different somewhere.
>
> > Are we implicitly relying on shared_type == CPUFREQ_SHARED_TYPE_HW to do
> > that for us?
> Right now we do, I believe, without - as said above - this being actually
> mandated by the spec.
HWP doesn't need ACPI data.  I wrote the driver according to the SDM, 
which is just MSRs.  It's Xen that needs ACPI data to initialize and use 
cpufreq.
Regardless of that, it looks like the checks for cpu_online() and 
performance_pminfo[] would constrain CPU accesses, so:
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>

Thanks,
Jason