1 // SPDX-License-Identifier: GPL-2.0-only
3 * itmt.c: Support Intel Turbo Boost Max Technology 3.0
5 * (C) Copyright 2016 Intel Corporation
6 * Author: Tim Chen <tim.c.chen@linux.intel.com>
8 * On platforms supporting Intel Turbo Boost Max Technology 3.0, (ITMT),
9 * the maximum turbo frequencies of some cores in a CPU package may be
10 * higher than for the other cores in the same package. In that case,
11 * better performance can be achieved by making the scheduler prefer
12 * to run tasks on the CPUs with higher max turbo frequencies.
14 * This file provides functions and data structures for enabling the
15 * scheduler to favor scheduling on cores can be boosted to a higher
16 * frequency under ITMT.
19 #include <linux/sched.h>
20 #include <linux/cpumask.h>
21 #include <linux/cpuset.h>
22 #include <linux/mutex.h>
23 #include <linux/sysctl.h>
24 #include <linux/nodemask.h>
26 static DEFINE_MUTEX(itmt_update_mutex);
27 DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);
29 /* Boolean to track if system has ITMT capabilities */
30 static bool __read_mostly sched_itmt_capable;
33 * Boolean to control whether we want to move processes to cpu capable
34 * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
37 * It can be set via /proc/sys/kernel/sched_itmt_enabled
39 unsigned int __read_mostly sysctl_sched_itmt_enabled;
41 static int sched_itmt_update_handler(struct ctl_table *table, int write,
42 void __user *buffer, size_t *lenp,
45 unsigned int old_sysctl;
48 mutex_lock(&itmt_update_mutex);
50 if (!sched_itmt_capable) {
51 mutex_unlock(&itmt_update_mutex);
55 old_sysctl = sysctl_sched_itmt_enabled;
56 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
58 if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
59 x86_topology_update = true;
60 rebuild_sched_domains();
63 mutex_unlock(&itmt_update_mutex);
68 static unsigned int zero;
69 static unsigned int one = 1;
70 static struct ctl_table itmt_kern_table[] = {
72 .procname = "sched_itmt_enabled",
73 .data = &sysctl_sched_itmt_enabled,
74 .maxlen = sizeof(unsigned int),
76 .proc_handler = sched_itmt_update_handler,
83 static struct ctl_table itmt_root_table[] = {
87 .child = itmt_kern_table,
92 static struct ctl_table_header *itmt_sysctl_header;
95 * sched_set_itmt_support() - Indicate platform supports ITMT
97 * This function is used by the OS to indicate to scheduler that the platform
98 * is capable of supporting the ITMT feature.
100 * The current scheme has the pstate driver detects if the system
101 * is ITMT capable and call sched_set_itmt_support.
103 * This must be done only after sched_set_itmt_core_prio
104 * has been called to set the cpus' priorities.
105 * It must not be called with cpu hot plug lock
106 * held as we need to acquire the lock to rebuild sched domains
109 * Return: 0 on success
111 int sched_set_itmt_support(void)
113 mutex_lock(&itmt_update_mutex);
115 if (sched_itmt_capable) {
116 mutex_unlock(&itmt_update_mutex);
120 itmt_sysctl_header = register_sysctl_table(itmt_root_table);
121 if (!itmt_sysctl_header) {
122 mutex_unlock(&itmt_update_mutex);
126 sched_itmt_capable = true;
128 sysctl_sched_itmt_enabled = 1;
130 x86_topology_update = true;
131 rebuild_sched_domains();
133 mutex_unlock(&itmt_update_mutex);
139 * sched_clear_itmt_support() - Revoke platform's support of ITMT
141 * This function is used by the OS to indicate that it has
142 * revoked the platform's support of ITMT feature.
144 * It must not be called with cpu hot plug lock
145 * held as we need to acquire the lock to rebuild sched domains
148 void sched_clear_itmt_support(void)
150 mutex_lock(&itmt_update_mutex);
152 if (!sched_itmt_capable) {
153 mutex_unlock(&itmt_update_mutex);
156 sched_itmt_capable = false;
158 if (itmt_sysctl_header) {
159 unregister_sysctl_table(itmt_sysctl_header);
160 itmt_sysctl_header = NULL;
163 if (sysctl_sched_itmt_enabled) {
164 /* disable sched_itmt if we are no longer ITMT capable */
165 sysctl_sched_itmt_enabled = 0;
166 x86_topology_update = true;
167 rebuild_sched_domains();
170 mutex_unlock(&itmt_update_mutex);
173 int arch_asym_cpu_priority(int cpu)
175 return per_cpu(sched_core_priority, cpu);
179 * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
180 * @prio: Priority of cpu core
181 * @core_cpu: The cpu number associated with the core
183 * The pstate driver will find out the max boost frequency
184 * and call this function to set a priority proportional
185 * to the max boost frequency. CPU with higher boost
186 * frequency will receive higher priority.
188 * No need to rebuild sched domain after updating
189 * the CPU priorities. The sched domains have no
190 * dependency on CPU priorities.
192 void sched_set_itmt_core_prio(int prio, int core_cpu)
196 for_each_cpu(cpu, topology_sibling_cpumask(core_cpu)) {
200 * Ensure that the siblings are moved to the end
201 * of the priority chain and only used when
202 * all other high priority cpus are out of capacity.
204 smt_prio = prio * smp_num_siblings / i;
205 per_cpu(sched_core_priority, cpu) = smt_prio;