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

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Date:	Thu, 7 Apr 2016 13:05:52 +0800
From:	Huang Rui <ray.huang@....com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	Jean Delvare <jdelvare@...e.de>, <linux-hwmon@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>,
	"Sherry Hurwitz" <sherry.hurwitz@....com>
Subject: Re: [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@...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