Re: [PATCH v2] xen/acpi: upload power and performance related data from a PVH dom0

[Jason Andryuk]

On 2024-09-25 05:17, Jürgen Groß wrote:
> On 16.09.24 22:50, Jason Andryuk wrote:
> > From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> >
> > When running as a PVH dom0 the ACPI MADT is crafted by Xen in order to
> > report the correct numbers of vCPUs that dom0 has, so the host MADT is
> > not provided to dom0.  This creates issues when parsing the power and
> > performance related data from ACPI dynamic tables, as the ACPI
> > Processor UIDs found on the dynamic code are likely to not match the
> > ones crafted by Xen in the dom0 MADT.
> >
> > Xen would rely on Linux having filled at least the power and
> > performance related data of the vCPUs on the system, and would clone
> > that information in order to setup the remaining pCPUs on the system
> > if dom0 vCPUs < pCPUs.  However when running as PVH dom0 it's likely
> > that none of dom0 CPUs will have the power and performance data
> > filled, and hence the Xen ACPI Processor driver needs to fetch that
> > information by itself.
> >
> > In order to do so correctly, introduce a new helper to fetch the _CST
> > data without taking into account the system capabilities from the
> > CPUID output, as the capabilities reported to dom0 in CPUID might be
> > different from the ones on the host.
> >
> > Note that the newly introduced code will only fetch the _CST, _PSS,
> > _PPC and _PCT from a single CPU, and clone that information for all the
> > other Processors.  This won't work on an heterogeneous system with
> > Processors having different power and performance related data between
> > them.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> > ---
> > v2:
> > Add second buffer for _CST.  Call was failing with
> > AE_BUFFER_OVERFLOW(0x000b)
> >
> > Running a PVH Dom0 on AMD, I needed this v2 change to get the C-State
> > information uploaded.
> >
> > ---
> >   drivers/xen/pcpu.c               |   3 +-
> >   drivers/xen/xen-acpi-processor.c | 230 ++++++++++++++++++++++++++++---
> >   include/xen/xen.h                |   2 +-
> >   3 files changed, 216 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/xen/pcpu.c b/drivers/xen/pcpu.c
> > index c63f317e3df3..dc9f2c14bf62 100644
> > --- a/drivers/xen/pcpu.c
> > +++ b/drivers/xen/pcpu.c
>
> ...
>
> > @@ -354,24 +511,44 @@ read_acpi_id(acpi_handle handle, u32 lvl, void 
> > *context, void **rv)
> >       default:
> >           return AE_OK;
> >       }
> > -    if (invalid_phys_cpuid(acpi_get_phys_id(handle,
> > -                        acpi_type == ACPI_TYPE_DEVICE,
> > -                        acpi_id))) {
> > +
> > +    if (!xen_processor_present(acpi_id)) {
> >           pr_debug("CPU with ACPI ID %u is unavailable\n", acpi_id);
> >           return AE_OK;
> >       }
> > -    /* There are more ACPI Processor objects than in x2APIC or MADT.
> > -     * This can happen with incorrect ACPI SSDT declerations. */
> > -    if (acpi_id >= nr_acpi_bits) {
> > -        pr_debug("max acpi id %u, trying to set %u\n",
> > -             nr_acpi_bits - 1, acpi_id);
> > -        return AE_OK;
> > -    }
> > +
> >       /* OK, There is a ACPI Processor object */
> >       __set_bit(acpi_id, acpi_id_present);
> >       pr_debug("ACPI CPU%u w/ PBLK:0x%lx\n", acpi_id, (unsigned 
> > long)pblk);
> > +    if (!pr_initialized) {
> > +        struct acpi_processor *pr = context;
> > +        int rc;
> > +
> > +        /*
> > +         * There's no CPU on the system that has any performance or
> > +         * power related data, initialize all the required fields by
> > +         * fetching that info here.
> > +         *
> > +         * Note such information is only fetched once, and then reused
> > +         * for all pCPUs.  This won't work on heterogeneous systems
> > +         * with different Cx anb/or Px states between CPUs.
> > +         */
> > +
> > +        pr->handle = handle;
> > +
> > +        rc = acpi_processor_get_performance_info(pr);
> > +        if (rc)
> > +            pr_debug("ACPI CPU%u failed to get performance data\n",
> > +                 acpi_id);
>
> Is it really normal to get a failure here? Shouldn't the reaction
> be a little bit more visible in this case?
>
> And can you just continue processing?
>
> > +        rc = xen_acpi_processor_evaluate_cst(handle, &pr->power);
> > +        if (rc)
> > +            pr_debug("ACPI CPU%u failed to get _CST data\n", acpi_id);
>
> Same again. Is pr_debug() enough?

Thanks.  I'll switch them to pr_err().  And I'll only set pr_initialized 
= true when both calls succeed.

Regards,
Jason