linux/arch/arm/kernel/topology.c

/*
 * arch/arm/kernel/topology.c
 *
 * Copyright (C) 2011 Linaro Limited.
 * Written by: Vincent Guittot
 *
 * based on arch/sh/kernel/topology.c
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */

#include <linux/arch_topology.h>
#include <linux/cpu.h>
#include <linux/cpufreq.h>
#include <linux/cpumask.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/node.h>
#include <linux/nodemask.h>
#include <linux/of.h>
#include <linux/sched.h>
#include <linux/sched/topology.h>
#include <linux/slab.h>
#include <linux/string.h>

#include <asm/cpu.h>
#include <asm/cputype.h>
#include <asm/topology.h>

/*
 * cpu capacity scale management
 */

/*
 * cpu capacity table
 * This per cpu data structure describes the relative capacity of each core.
 * On a heteregenous system, cores don't have the same computation capacity
 * and we reflect that difference in the cpu_capacity field so the scheduler
 * can take this difference into account during load balance. A per cpu
 * structure is preferred because each CPU updates its own cpu_capacity field
 * during the load balance except for idle cores. One idle core is selected
 * to run the rebalance_domains for all idle cores and the cpu_capacity can be
 * updated during this sequence.
 */

#ifdef CONFIG_OF
struct cpu_efficiency {
	const char *compatible;
	unsigned long efficiency;
};

/*
 * Table of relative efficiency of each processors
 * The efficiency value must fit in 20bit and the final
 * cpu_scale value must be in the range
 *   0 < cpu_scale < 3*SCHED_CAPACITY_SCALE/2
 * in order to return at most 1 when DIV_ROUND_CLOSEST
 * is used to compute the capacity of a CPU.
 * Processors that are not defined in the table,
 * use the default SCHED_CAPACITY_SCALE value for cpu_scale.
 */
static const struct cpu_efficiency table_efficiency[] = {
	{"arm,cortex-a15", 3891},
	{"arm,cortex-a7",  2048},
	{NULL, },
};

static unsigned long *__cpu_capacity;
#define cpu_capacity(cpu)	__cpu_capacity[cpu]

static unsigned long middle_capacity = 1;
static bool cap_from_dt = true;

/*
 * Iterate all CPUs' descriptor in DT and compute the efficiency
 * (as per table_efficiency). Also calculate a middle efficiency
 * as close as possible to  (max{eff_i} - min{eff_i}) / 2
 * This is later used to scale the cpu_capacity field such that an
 * 'average' CPU is of middle capacity. Also see the comments near
 * table_efficiency[] and update_cpu_capacity().
 */
static void __init parse_dt_topology(void)
{
	const struct cpu_efficiency *cpu_eff;
	struct device_node *cn = NULL;
	unsigned long min_capacity = ULONG_MAX;
	unsigned long max_capacity = 0;
	unsigned long capacity = 0;
	int cpu = 0;

	__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
				 GFP_NOWAIT);

	for_each_possible_cpu(cpu) {
		const __be32 *rate;
		int len;

		/* too early to use cpu->of_node */
		cn = of_get_cpu_node(cpu, NULL);
		if (!cn) {
			pr_err("missing device node for CPU %d\n", cpu);
			continue;
		}

		if (topology_parse_cpu_capacity(cn, cpu)) {
			of_node_put(cn);
			continue;
		}

		cap_from_dt = false;

		for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
			if (of_device_is_compatible(cn, cpu_eff->compatible))
				break;

		if (cpu_eff->compatible == NULL)
			continue;

		rate = of_get_property(cn, "clock-frequency", &len);
		if (!rate || len != 4) {
			pr_err("%pOF missing clock-frequency property\n", cn);
			continue;
		}

		capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;

		/* Save min capacity of the system */
		if (capacity < min_capacity)
			min_capacity = capacity;

		/* Save max capacity of the system */
		if (capacity > max_capacity)
			max_capacity = capacity;

		cpu_capacity(cpu) = capacity;
	}

	/* If min and max capacities are equals, we bypass the update of the
	 * cpu_scale because all CPUs have the same capacity. Otherwise, we
	 * compute a middle_capacity factor that will ensure that the capacity
	 * of an 'average' CPU of the system will be as close as possible to
	 * SCHED_CAPACITY_SCALE, which is the default value, but with the
	 * constraint explained near table_efficiency[].
	 */
	if (4*max_capacity < (3*(max_capacity + min_capacity)))
		middle_capacity = (min_capacity + max_capacity)
				>> (SCHED_CAPACITY_SHIFT+1);
	else
		middle_capacity = ((max_capacity / 3)
				>> (SCHED_CAPACITY_SHIFT-1)) + 1;

	if (cap_from_dt)
		topology_normalize_cpu_scale();
}

/*
 * Look for a customed capacity of a CPU in the cpu_capacity table during the
 * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
 * function returns directly for SMP system.
 */
static void update_cpu_capacity(unsigned int cpu)
{
	if (!cpu_capacity(cpu) || cap_from_dt)
		return;

	topology_set_cpu_scale(cpu, cpu_capacity(cpu) / middle_capacity);

	pr_info("CPU%u: update cpu_capacity %lu\n",
		cpu, topology_get_cpu_scale(cpu));
}

#else
static inline void parse_dt_topology(void) {}
static inline void update_cpu_capacity(unsigned int cpuid) {}
#endif

/*
 * store_cpu_topology is called at boot when only one cpu is running
 * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
 * which prevents simultaneous write access to cpu_topology array
 */
void store_cpu_topology(unsigned int cpuid)
{
	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
	unsigned int mpidr;

	if (cpuid_topo->package_id != -1)
		goto topology_populated;

	mpidr = read_cpuid_mpidr();

	/* create cpu topology mapping */
	if ((mpidr & MPIDR_SMP_BITMASK) == MPIDR_SMP_VALUE) {
		/*
		 * This is a multiprocessor system
		 * multiprocessor format & multiprocessor mode field are set
		 */

		if (mpidr & MPIDR_MT_BITMASK) {
			/* core performance interdependency */
			cpuid_topo->thread_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
			cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
			cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
		} else {
			/* largely independent cores */
			cpuid_topo->thread_id = -1;
			cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
			cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
		}
	} else {
		/*
		 * This is an uniprocessor system
		 * we are in multiprocessor format but uniprocessor system
		 * or in the old uniprocessor format
		 */
		cpuid_topo->thread_id = -1;
		cpuid_topo->core_id = 0;
		cpuid_topo->package_id = -1;
	}

	update_cpu_capacity(cpuid);

	pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
		cpuid, cpu_topology[cpuid].thread_id,
		cpu_topology[cpuid].core_id,
		cpu_topology[cpuid].package_id, mpidr);

topology_populated:
	update_siblings_masks(cpuid);
}

/*
 * init_cpu_topology is called at boot when only one cpu is running
 * which prevent simultaneous write access to cpu_topology array
 */
void __init init_cpu_topology(void)
{
	reset_cpu_topology();
	smp_wmb();

	parse_dt_topology();
}