[PATCH v3 1/1] perf: arm_pmuv3: Don't use PMCCNTR_EL0 on SMT cores

[Mark Brown]

On Mon, Sep 22, 2025 at 11:30:10AM +0800, Yicong Yang wrote:

> index d72d6e5aa200..daa1af2e8204 100644
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -89,6 +89,17 @@ void remove_cpu_topology(unsigned int cpuid);
>  void reset_cpu_topology(void);
>  int parse_acpi_topology(void);
>  void freq_inv_set_max_ratio(int cpu, u64 max_rate);
> +
> +/*
> + * Architectures like ARM64 don't have reliable architectural way to get SMT
> + * information and depend on the firmware (ACPI/OF) report. Non-SMT core won't
> + * initialize thread_id so we can use this to detect the SMT implementation.
> + */
> +static inline bool topology_core_has_smt(int cpu)
> +{
> +	return cpu_topology[cpu].thread_id != -1;
> +}

I'm seeing build failures in -next on arm v5 and v6:

/build/stage/linux/drivers/perf/arm_pmu.c: In function ‘armpmu_register’:
/build/stage/linux/drivers/perf/arm_pmu.c:935:24: error: implicit declaration of
 function ‘topology_core_has_smt’; did you mean ‘topology_core_cpumask’? [-Wimpl
icit-function-declaration]
  935 |         pmu->has_smt = topology_core_has_smt(cpumask_first(&pmu->support
ed_cpus));
      |                        ^~~~~~~~~~~~~~~~~~~~~
      |                        topology_core_cpumask
make[5]: *** [/build/stage/linux/scripts/Makefile.build:287: drivers/perf/arm_pm
u.o] Error 1

The above function is inside a CONFIG_GENERIC_ARCH_TOPOLOGY guard, we
need a stub definition for architectures which don't have topology
support or for the users to have guards.
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