Re: [PATCH v6 2/6] hwmon: (fam15h_power) Add compute unit accumulated power

Huang Rui
2016-04-07T05:04:39Z

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