/*
* Timer events oriented CPU idle governor
*
- * TEO governor:
* Copyright (C) 2018 - 2021 Intel Corporation
* Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
- *
- * Util-awareness mechanism:
- * Copyright (C) 2022 Arm Ltd.
- * Author: Kajetan Puchalski <kajetan.puchalski@arm.com>
*/
/**
* select the given idle state instead of the candidate one.
*
* 3. By default, select the candidate state.
- *
- * Util-awareness mechanism:
- *
- * The idea behind the util-awareness extension is that there are two distinct
- * scenarios for the CPU which should result in two different approaches to idle
- * state selection - utilized and not utilized.
- *
- * In this case, 'utilized' means that the average runqueue util of the CPU is
- * above a certain threshold.
- *
- * When the CPU is utilized while going into idle, more likely than not it will
- * be woken up to do more work soon and so a shallower idle state should be
- * selected to minimise latency and maximise performance. When the CPU is not
- * being utilized, the usual metrics-based approach to selecting the deepest
- * available idle state should be preferred to take advantage of the power
- * saving.
- *
- * In order to achieve this, the governor uses a utilization threshold.
- * The threshold is computed per-CPU as a percentage of the CPU's capacity
- * by bit shifting the capacity value. Based on testing, the shift of 6 (~1.56%)
- * seems to be getting the best results.
- *
- * Before selecting the next idle state, the governor compares the current CPU
- * util to the precomputed util threshold. If it's below, it defaults to the
- * TEO metrics mechanism. If it's above, the closest shallower idle state will
- * be selected instead, as long as is not a polling state.
*/
#include <linux/cpuidle.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
-#include <linux/sched.h>
#include <linux/sched/clock.h>
-#include <linux/sched/topology.h>
#include <linux/tick.h>
#include "gov.h"
-/*
- * The number of bits to shift the CPU's capacity by in order to determine
- * the utilized threshold.
- *
- * 6 was chosen based on testing as the number that achieved the best balance
- * of power and performance on average.
- *
- * The resulting threshold is high enough to not be triggered by background
- * noise and low enough to react quickly when activity starts to ramp up.
- */
-#define UTIL_THRESHOLD_SHIFT 6
-
/*
* The PULSE value is added to metrics when they grow and the DECAY_SHIFT value
* is used for decreasing metrics on a regular basis.
* @next_recent_idx: Index of the next @recent_idx entry to update.
* @recent_idx: Indices of bins corresponding to recent "intercepts".
* @tick_hits: Number of "hits" after TICK_NSEC.
- * @util_threshold: Threshold above which the CPU is considered utilized
*/
struct teo_cpu {
s64 time_span_ns;
int next_recent_idx;
int recent_idx[NR_RECENT];
unsigned int tick_hits;
- unsigned long util_threshold;
};
static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
-/**
- * teo_cpu_is_utilized - Check if the CPU's util is above the threshold
- * @cpu: Target CPU
- * @cpu_data: Governor CPU data for the target CPU
- */
-#ifdef CONFIG_SMP
-static bool teo_cpu_is_utilized(int cpu, struct teo_cpu *cpu_data)
-{
- return sched_cpu_util(cpu) > cpu_data->util_threshold;
-}
-#else
-static bool teo_cpu_is_utilized(int cpu, struct teo_cpu *cpu_data)
-{
- return false;
-}
-#endif
-
/**
* teo_update - Update CPU metrics after wakeup.
* @drv: cpuidle driver containing state data.
int constraint_idx = 0;
int idx0 = 0, idx = -1;
bool alt_intercepts, alt_recent;
- bool cpu_utilized;
s64 duration_ns;
int i;
if (!dev->states_usage[0].disable)
idx = 0;
- cpu_utilized = teo_cpu_is_utilized(dev->cpu, cpu_data);
- /*
- * If the CPU is being utilized over the threshold and there are only 2
- * states to choose from, the metrics need not be considered, so choose
- * the shallowest non-polling state and exit.
- */
- if (drv->state_count < 3 && cpu_utilized) {
- /*
- * If state 0 is enabled and it is not a polling one, select it
- * right away unless the scheduler tick has been stopped, in
- * which case care needs to be taken to leave the CPU in a deep
- * enough state in case it is not woken up any time soon after
- * all. If state 1 is disabled, though, state 0 must be used
- * anyway.
- */
- if ((!idx && !(drv->states[0].flags & CPUIDLE_FLAG_POLLING) &&
- teo_state_ok(0, drv)) || dev->states_usage[1].disable) {
- idx = 0;
- goto out_tick;
- }
- /* Assume that state 1 is not a polling one and use it. */
- idx = 1;
- duration_ns = drv->states[1].target_residency_ns;
- goto end;
- }
-
/* Compute the sums of metrics for early wakeup pattern detection. */
for (i = 1; i < drv->state_count; i++) {
struct teo_bin *prev_bin = &cpu_data->state_bins[i-1];
if (idx > constraint_idx)
idx = constraint_idx;
- /*
- * If the CPU is being utilized over the threshold, choose a shallower
- * non-polling state to improve latency, unless the scheduler tick has
- * been stopped already and the shallower state's target residency is
- * not sufficiently large.
- */
- if (cpu_utilized) {
- i = teo_find_shallower_state(drv, dev, idx, KTIME_MAX, true);
- if (teo_state_ok(i, drv))
- idx = i;
- }
-
/*
* Skip the timers check if state 0 is the current candidate one,
* because an immediate non-timer wakeup is expected in that case.
struct cpuidle_device *dev)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
- unsigned long max_capacity = arch_scale_cpu_capacity(dev->cpu);
int i;
memset(cpu_data, 0, sizeof(*cpu_data));
- cpu_data->util_threshold = max_capacity >> UTIL_THRESHOLD_SHIFT;
for (i = 0; i < NR_RECENT; i++)
cpu_data->recent_idx[i] = -1;
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