1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * itmt.c: Support Intel Turbo Boost Max Technology 3.0
4 *
5 * (C) Copyright 2016 Intel Corporation
6 * Author: Tim Chen <tim.c.chen@linux.intel.com>
7 *
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.
13 *
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.
17 */
18
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>
25
26 static DEFINE_MUTEX(itmt_update_mutex);
27 DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);
28
29 /* Boolean to track if system has ITMT capabilities */
30 static bool __read_mostly sched_itmt_capable;
31
32 /*
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
35 * Technology 3.0.
36 *
37 * It can be set via /proc/sys/kernel/sched_itmt_enabled
38 */
39 unsigned int __read_mostly sysctl_sched_itmt_enabled;
40
41 static int sched_itmt_update_handler(const struct ctl_table *table, int write,
42 void *buffer, size_t *lenp, loff_t *ppos)
43 {
44 unsigned int old_sysctl;
45 int ret;
46
47 mutex_lock(&itmt_update_mutex);
48
49 if (!sched_itmt_capable) {
50 mutex_unlock(&itmt_update_mutex);
51 return -EINVAL;
52 }
53
54 old_sysctl = sysctl_sched_itmt_enabled;
55 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
56
57 if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
58 x86_topology_update = true;
59 rebuild_sched_domains();
60 }
61
62 mutex_unlock(&itmt_update_mutex);
63
64 return ret;
65 }
66
67 static struct ctl_table itmt_kern_table[] = {
68 {
69 .procname = "sched_itmt_enabled",
70 .data = &sysctl_sched_itmt_enabled,
71 .maxlen = sizeof(unsigned int),
72 .mode = 0644,
73 .proc_handler = sched_itmt_update_handler,
74 .extra1 = SYSCTL_ZERO,
75 .extra2 = SYSCTL_ONE,
76 },
77 };
78
79 static struct ctl_table_header *itmt_sysctl_header;
80
81 /**
82 * sched_set_itmt_support() - Indicate platform supports ITMT
83 *
84 * This function is used by the OS to indicate to scheduler that the platform
85 * is capable of supporting the ITMT feature.
86 *
87 * The current scheme has the pstate driver detects if the system
88 * is ITMT capable and call sched_set_itmt_support.
89 *
90 * This must be done only after sched_set_itmt_core_prio
91 * has been called to set the cpus' priorities.
92 * It must not be called with cpu hot plug lock
93 * held as we need to acquire the lock to rebuild sched domains
94 * later.
95 *
96 * Return: 0 on success
97 */
98 int sched_set_itmt_support(void)
99 {
100 mutex_lock(&itmt_update_mutex);
101
102 if (sched_itmt_capable) {
103 mutex_unlock(&itmt_update_mutex);
104 return 0;
105 }
106
107 itmt_sysctl_header = register_sysctl("kernel", itmt_kern_table);
108 if (!itmt_sysctl_header) {
109 mutex_unlock(&itmt_update_mutex);
110 return -ENOMEM;
111 }
112
113 sched_itmt_capable = true;
114
115 sysctl_sched_itmt_enabled = 1;
116
117 x86_topology_update = true;
118 rebuild_sched_domains();
119
120 mutex_unlock(&itmt_update_mutex);
121
122 return 0;
123 }
124
125 /**
126 * sched_clear_itmt_support() - Revoke platform's support of ITMT
127 *
128 * This function is used by the OS to indicate that it has
129 * revoked the platform's support of ITMT feature.
130 *
131 * It must not be called with cpu hot plug lock
132 * held as we need to acquire the lock to rebuild sched domains
133 * later.
134 */
135 void sched_clear_itmt_support(void)
136 {
137 mutex_lock(&itmt_update_mutex);
138
139 if (!sched_itmt_capable) {
140 mutex_unlock(&itmt_update_mutex);
141 return;
142 }
143 sched_itmt_capable = false;
144
145 if (itmt_sysctl_header) {
146 unregister_sysctl_table(itmt_sysctl_header);
147 itmt_sysctl_header = NULL;
148 }
149
150 if (sysctl_sched_itmt_enabled) {
151 /* disable sched_itmt if we are no longer ITMT capable */
152 sysctl_sched_itmt_enabled = 0;
153 x86_topology_update = true;
154 rebuild_sched_domains();
155 }
156
157 mutex_unlock(&itmt_update_mutex);
158 }
159
160 int arch_asym_cpu_priority(int cpu)
161 {
162 return per_cpu(sched_core_priority, cpu);
163 }
164
165 /**
166 * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
167 * @prio: Priority of @cpu
168 * @cpu: The CPU number
169 *
170 * The pstate driver will find out the max boost frequency
171 * and call this function to set a priority proportional
172 * to the max boost frequency. CPUs with higher boost
173 * frequency will receive higher priority.
174 *
175 * No need to rebuild sched domain after updating
176 * the CPU priorities. The sched domains have no
177 * dependency on CPU priorities.
178 */
179 void sched_set_itmt_core_prio(int prio, int cpu)
180 {
181 per_cpu(sched_core_priority, cpu) = prio;
182 }
183
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