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    SubjectRe: [PATCH v6 2/6] hwmon: (fam15h_power) Add compute unit accumulated power
    On Wed, Apr 06, 2016 at 08:30:25AM -0700, Guenter Roeck wrote:
    > On Wed, Apr 06, 2016 at 03:44:11PM +0800, Huang Rui wrote:
    > >
    > > +static void do_read_registers_on_cu(void *_data)
    > > +{
    > > + struct fam15h_power_data *data = _data;
    > > + int cpu, cu;
    > > +
    > > + cpu = smp_processor_id();
    > > +
    >
    > Is this function now defined in non-SMP code ? If so, can you point me to the
    > patch or branch introducing it ? It doesn't seem to be in mainline or in -next
    > unless I am missing it.
    >

    In include/linux/smp.h


    #else /* !SMP */

    static inline void smp_send_stop(void) { }

    /*
    * These macros fold the SMP functionality into a single CPU system
    */
    #define raw_smp_processor_id() 0

    ...

    /*
    * smp_processor_id(): get the current CPU ID.
    *
    * if DEBUG_PREEMPT is enabled then we check whether it is
    * used in a preemption-safe way. (smp_processor_id() is safe
    * if it's used in a preemption-off critical section, or in
    * a thread that is bound to the current CPU.)
    *
    * NOTE: raw_smp_processor_id() is for internal use only
    * (smp_processor_id() is the preferred variant), but in rare
    * instances it might also be used to turn off false positives
    * (i.e. smp_processor_id() use that the debugging code reports but
    * which use for some reason is legal). Don't use this to hack around
    * the warning message, as your code might not work under PREEMPT.
    */
    #ifdef CONFIG_DEBUG_PREEMPT
    extern unsigned int debug_smp_processor_id(void);
    # define smp_processor_id() debug_smp_processor_id()
    #else
    # define smp_processor_id() raw_smp_processor_id()
    #endif


    Actually smp_processor_id() should returns 0 if we disable CONFIG_SMP.

    > > + /*
    > > + * With the new x86 topology modelling, cpu core id actually
    > > + * is compute unit id.
    > > + */
    > > + cu = cpu_data(cpu).cpu_core_id;
    > > +
    > > + rdmsrl_safe(MSR_F15H_CU_PWR_ACCUMULATOR, &data->cu_acc_power[cu]);
    > > +}
    > > +
    > > +/*
    > > + * This function is only able to be called when CPUID
    > > + * Fn8000_0007:EDX[12] is set.
    > > + */
    > > +static int read_registers(struct fam15h_power_data *data)
    > > +{
    > > + int this_cpu, ret, cpu;
    > > + int core, this_core;
    > > + cpumask_var_t mask;
    > > +
    > > + ret = zalloc_cpumask_var(&mask, GFP_KERNEL);
    > > + if (!ret)
    > > + return -ENOMEM;
    > > +
    > > + get_online_cpus();
    > > + this_cpu = smp_processor_id();
    > > +
    > > + /*
    > > + * Choose the first online core of each compute unit, and then
    > > + * read their MSR value of power and ptsc in a single IPI,
    > > + * because the MSR value of CPU core represent the compute
    > > + * unit's.
    > > + */
    > > + core = -1;
    > > +
    > > + for_each_online_cpu(cpu) {
    > > + this_core = topology_core_id(cpu);
    > > +
    > > + if (this_core == core)
    > > + continue;
    > > +
    > > + core = this_core;
    > > +
    > Sorry if I missed some context - is it guaranteed that all cores in the same
    > compute unit are returned next to each other from for_each_online_cpu() ?
    >

    Yes, there is a documentation which introduced from v4.6-rc2:
    https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f7be8610bca88e59dd2fd5d98fcbc5031ef0e079

    - topology_core_id();

    The ID of the core to which a thread belongs. It is also printed in /proc/cpuinfo
    "core_id."

    ...

    AMD nomenclature for CMT systems:

    [node 0] -> [Compute Unit 0] -> [Compute Unit Core 0] -> Linux CPU 0
    -> [Compute Unit Core 1] -> Linux CPU 1
    -> [Compute Unit 1] -> [Compute Unit Core 0] -> Linux CPU 2
    -> [Compute Unit Core 1] -> Linux CPU 3

    ray@hr-ub:~/tip$ cat /proc/cpuinfo | grep "core id"
    core id : 0
    core id : 0
    core id : 1
    core id : 1

    "this_core" here actually means the [Compute Unit] id which current
    [Compute Unit Core] belongs to. And "cpu" here means the [Compute Unit Core].

    Thanks,
    Rui

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