linux/kernel/power/energy_model.c
Lukasz Luba ae6ccaa650 PM: EM: convert power field to micro-Watts precision and align drivers
The milli-Watts precision causes rounding errors while calculating
efficiency cost for each OPP. This is especially visible in the 'simple'
Energy Model (EM), where the power for each OPP is provided from OPP
framework. This can cause some OPPs to be marked inefficient, while
using micro-Watts precision that might not happen.

Update all EM users which access 'power' field and assume the value is
in milli-Watts.

Solve also an issue with potential overflow in calculation of energy
estimation on 32bit machine. It's needed now since the power value
(thus the 'cost' as well) are higher.

Example calculation which shows the rounding error and impact:

power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz

power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000
power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18

power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961
power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21

max_freq = 2000MHz

cost_a_mW = 18 * 2000MHz/500MHz = 72
cost_a_uW = 18000 * 2000MHz/500MHz = 72000

cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better
cost_b_uW = 21961 * 2000MHz/600MHz = 73203

The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly
better that the 'cost_b_uW' (this patch uses micro-Watts) and such
would have impact on the 'inefficient OPPs' information in the Cpufreq
framework. This patch set removes the rounding issue.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2022-07-15 19:17:30 +02:00

442 lines
10 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Energy Model of devices
*
* Copyright (c) 2018-2021, Arm ltd.
* Written by: Quentin Perret, Arm ltd.
* Improvements provided by: Lukasz Luba, Arm ltd.
*/
#define pr_fmt(fmt) "energy_model: " fmt
#include <linux/cpu.h>
#include <linux/cpufreq.h>
#include <linux/cpumask.h>
#include <linux/debugfs.h>
#include <linux/energy_model.h>
#include <linux/sched/topology.h>
#include <linux/slab.h>
/*
* Mutex serializing the registrations of performance domains and letting
* callbacks defined by drivers sleep.
*/
static DEFINE_MUTEX(em_pd_mutex);
static bool _is_cpu_device(struct device *dev)
{
return (dev->bus == &cpu_subsys);
}
#ifdef CONFIG_DEBUG_FS
static struct dentry *rootdir;
static void em_debug_create_ps(struct em_perf_state *ps, struct dentry *pd)
{
struct dentry *d;
char name[24];
snprintf(name, sizeof(name), "ps:%lu", ps->frequency);
/* Create per-ps directory */
d = debugfs_create_dir(name, pd);
debugfs_create_ulong("frequency", 0444, d, &ps->frequency);
debugfs_create_ulong("power", 0444, d, &ps->power);
debugfs_create_ulong("cost", 0444, d, &ps->cost);
debugfs_create_ulong("inefficient", 0444, d, &ps->flags);
}
static int em_debug_cpus_show(struct seq_file *s, void *unused)
{
seq_printf(s, "%*pbl\n", cpumask_pr_args(to_cpumask(s->private)));
return 0;
}
DEFINE_SHOW_ATTRIBUTE(em_debug_cpus);
static int em_debug_flags_show(struct seq_file *s, void *unused)
{
struct em_perf_domain *pd = s->private;
seq_printf(s, "%#lx\n", pd->flags);
return 0;
}
DEFINE_SHOW_ATTRIBUTE(em_debug_flags);
static void em_debug_create_pd(struct device *dev)
{
struct dentry *d;
int i;
/* Create the directory of the performance domain */
d = debugfs_create_dir(dev_name(dev), rootdir);
if (_is_cpu_device(dev))
debugfs_create_file("cpus", 0444, d, dev->em_pd->cpus,
&em_debug_cpus_fops);
debugfs_create_file("flags", 0444, d, dev->em_pd,
&em_debug_flags_fops);
/* Create a sub-directory for each performance state */
for (i = 0; i < dev->em_pd->nr_perf_states; i++)
em_debug_create_ps(&dev->em_pd->table[i], d);
}
static void em_debug_remove_pd(struct device *dev)
{
struct dentry *debug_dir;
debug_dir = debugfs_lookup(dev_name(dev), rootdir);
debugfs_remove_recursive(debug_dir);
}
static int __init em_debug_init(void)
{
/* Create /sys/kernel/debug/energy_model directory */
rootdir = debugfs_create_dir("energy_model", NULL);
return 0;
}
fs_initcall(em_debug_init);
#else /* CONFIG_DEBUG_FS */
static void em_debug_create_pd(struct device *dev) {}
static void em_debug_remove_pd(struct device *dev) {}
#endif
static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
int nr_states, struct em_data_callback *cb,
unsigned long flags)
{
unsigned long power, freq, prev_freq = 0, prev_cost = ULONG_MAX;
struct em_perf_state *table;
int i, ret;
u64 fmax;
table = kcalloc(nr_states, sizeof(*table), GFP_KERNEL);
if (!table)
return -ENOMEM;
/* Build the list of performance states for this performance domain */
for (i = 0, freq = 0; i < nr_states; i++, freq++) {
/*
* active_power() is a driver callback which ceils 'freq' to
* lowest performance state of 'dev' above 'freq' and updates
* 'power' and 'freq' accordingly.
*/
ret = cb->active_power(dev, &power, &freq);
if (ret) {
dev_err(dev, "EM: invalid perf. state: %d\n",
ret);
goto free_ps_table;
}
/*
* We expect the driver callback to increase the frequency for
* higher performance states.
*/
if (freq <= prev_freq) {
dev_err(dev, "EM: non-increasing freq: %lu\n",
freq);
goto free_ps_table;
}
/*
* The power returned by active_state() is expected to be
* positive and be in range.
*/
if (!power || power > EM_MAX_POWER) {
dev_err(dev, "EM: invalid power: %lu\n",
power);
goto free_ps_table;
}
table[i].power = power;
table[i].frequency = prev_freq = freq;
}
/* Compute the cost of each performance state. */
fmax = (u64) table[nr_states - 1].frequency;
for (i = nr_states - 1; i >= 0; i--) {
unsigned long power_res, cost;
if (flags & EM_PERF_DOMAIN_ARTIFICIAL) {
ret = cb->get_cost(dev, table[i].frequency, &cost);
if (ret || !cost || cost > EM_MAX_POWER) {
dev_err(dev, "EM: invalid cost %lu %d\n",
cost, ret);
goto free_ps_table;
}
} else {
power_res = table[i].power;
cost = div64_u64(fmax * power_res, table[i].frequency);
}
table[i].cost = cost;
if (table[i].cost >= prev_cost) {
table[i].flags = EM_PERF_STATE_INEFFICIENT;
dev_dbg(dev, "EM: OPP:%lu is inefficient\n",
table[i].frequency);
} else {
prev_cost = table[i].cost;
}
}
pd->table = table;
pd->nr_perf_states = nr_states;
return 0;
free_ps_table:
kfree(table);
return -EINVAL;
}
static int em_create_pd(struct device *dev, int nr_states,
struct em_data_callback *cb, cpumask_t *cpus,
unsigned long flags)
{
struct em_perf_domain *pd;
struct device *cpu_dev;
int cpu, ret, num_cpus;
if (_is_cpu_device(dev)) {
num_cpus = cpumask_weight(cpus);
/* Prevent max possible energy calculation to not overflow */
if (num_cpus > EM_MAX_NUM_CPUS) {
dev_err(dev, "EM: too many CPUs, overflow possible\n");
return -EINVAL;
}
pd = kzalloc(sizeof(*pd) + cpumask_size(), GFP_KERNEL);
if (!pd)
return -ENOMEM;
cpumask_copy(em_span_cpus(pd), cpus);
} else {
pd = kzalloc(sizeof(*pd), GFP_KERNEL);
if (!pd)
return -ENOMEM;
}
ret = em_create_perf_table(dev, pd, nr_states, cb, flags);
if (ret) {
kfree(pd);
return ret;
}
if (_is_cpu_device(dev))
for_each_cpu(cpu, cpus) {
cpu_dev = get_cpu_device(cpu);
cpu_dev->em_pd = pd;
}
dev->em_pd = pd;
return 0;
}
static void em_cpufreq_update_efficiencies(struct device *dev)
{
struct em_perf_domain *pd = dev->em_pd;
struct em_perf_state *table;
struct cpufreq_policy *policy;
int found = 0;
int i;
if (!_is_cpu_device(dev) || !pd)
return;
policy = cpufreq_cpu_get(cpumask_first(em_span_cpus(pd)));
if (!policy) {
dev_warn(dev, "EM: Access to CPUFreq policy failed");
return;
}
table = pd->table;
for (i = 0; i < pd->nr_perf_states; i++) {
if (!(table[i].flags & EM_PERF_STATE_INEFFICIENT))
continue;
if (!cpufreq_table_set_inefficient(policy, table[i].frequency))
found++;
}
cpufreq_cpu_put(policy);
if (!found)
return;
/*
* Efficiencies have been installed in CPUFreq, inefficient frequencies
* will be skipped. The EM can do the same.
*/
pd->flags |= EM_PERF_DOMAIN_SKIP_INEFFICIENCIES;
}
/**
* em_pd_get() - Return the performance domain for a device
* @dev : Device to find the performance domain for
*
* Returns the performance domain to which @dev belongs, or NULL if it doesn't
* exist.
*/
struct em_perf_domain *em_pd_get(struct device *dev)
{
if (IS_ERR_OR_NULL(dev))
return NULL;
return dev->em_pd;
}
EXPORT_SYMBOL_GPL(em_pd_get);
/**
* em_cpu_get() - Return the performance domain for a CPU
* @cpu : CPU to find the performance domain for
*
* Returns the performance domain to which @cpu belongs, or NULL if it doesn't
* exist.
*/
struct em_perf_domain *em_cpu_get(int cpu)
{
struct device *cpu_dev;
cpu_dev = get_cpu_device(cpu);
if (!cpu_dev)
return NULL;
return em_pd_get(cpu_dev);
}
EXPORT_SYMBOL_GPL(em_cpu_get);
/**
* em_dev_register_perf_domain() - Register the Energy Model (EM) for a device
* @dev : Device for which the EM is to register
* @nr_states : Number of performance states to register
* @cb : Callback functions providing the data of the Energy Model
* @cpus : Pointer to cpumask_t, which in case of a CPU device is
* obligatory. It can be taken from i.e. 'policy->cpus'. For other
* type of devices this should be set to NULL.
* @microwatts : Flag indicating that the power values are in micro-Watts or
* in some other scale. It must be set properly.
*
* Create Energy Model tables for a performance domain using the callbacks
* defined in cb.
*
* The @microwatts is important to set with correct value. Some kernel
* sub-systems might rely on this flag and check if all devices in the EM are
* using the same scale.
*
* If multiple clients register the same performance domain, all but the first
* registration will be ignored.
*
* Return 0 on success
*/
int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
struct em_data_callback *cb, cpumask_t *cpus,
bool microwatts)
{
unsigned long cap, prev_cap = 0;
unsigned long flags = 0;
int cpu, ret;
if (!dev || !nr_states || !cb)
return -EINVAL;
/*
* Use a mutex to serialize the registration of performance domains and
* let the driver-defined callback functions sleep.
*/
mutex_lock(&em_pd_mutex);
if (dev->em_pd) {
ret = -EEXIST;
goto unlock;
}
if (_is_cpu_device(dev)) {
if (!cpus) {
dev_err(dev, "EM: invalid CPU mask\n");
ret = -EINVAL;
goto unlock;
}
for_each_cpu(cpu, cpus) {
if (em_cpu_get(cpu)) {
dev_err(dev, "EM: exists for CPU%d\n", cpu);
ret = -EEXIST;
goto unlock;
}
/*
* All CPUs of a domain must have the same
* micro-architecture since they all share the same
* table.
*/
cap = arch_scale_cpu_capacity(cpu);
if (prev_cap && prev_cap != cap) {
dev_err(dev, "EM: CPUs of %*pbl must have the same capacity\n",
cpumask_pr_args(cpus));
ret = -EINVAL;
goto unlock;
}
prev_cap = cap;
}
}
if (microwatts)
flags |= EM_PERF_DOMAIN_MICROWATTS;
else if (cb->get_cost)
flags |= EM_PERF_DOMAIN_ARTIFICIAL;
ret = em_create_pd(dev, nr_states, cb, cpus, flags);
if (ret)
goto unlock;
dev->em_pd->flags |= flags;
em_cpufreq_update_efficiencies(dev);
em_debug_create_pd(dev);
dev_info(dev, "EM: created perf domain\n");
unlock:
mutex_unlock(&em_pd_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
/**
* em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device
* @dev : Device for which the EM is registered
*
* Unregister the EM for the specified @dev (but not a CPU device).
*/
void em_dev_unregister_perf_domain(struct device *dev)
{
if (IS_ERR_OR_NULL(dev) || !dev->em_pd)
return;
if (_is_cpu_device(dev))
return;
/*
* The mutex separates all register/unregister requests and protects
* from potential clean-up/setup issues in the debugfs directories.
* The debugfs directory name is the same as device's name.
*/
mutex_lock(&em_pd_mutex);
em_debug_remove_pd(dev);
kfree(dev->em_pd->table);
kfree(dev->em_pd);
dev->em_pd = NULL;
mutex_unlock(&em_pd_mutex);
}
EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);