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(struct ctl_table *table, int write,
42 void __user *buffer, size_t *lenp,
43 loff_t *ppos)
44 {
45 unsigned int old_sysctl;
46 int ret;
47
48 mutex_lock(&itmt_update_mutex);
49
50 if (!sched_itmt_capable) {
51 mutex_unlock(&itmt_update_mutex);
52 return -EINVAL;
53 }
54
55 old_sysctl = sysctl_sched_itmt_enabled;
56 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
57
58 if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
59 x86_topology_update = true;
60 rebuild_sched_domains();
61 }
62
63 mutex_unlock(&itmt_update_mutex);
64
65 return ret;
66 }
67
68 static struct ctl_table itmt_kern_table[] = {
69 {
70 .procname = "sched_itmt_enabled",
71 .data = &sysctl_sched_itmt_enabled,
72 .maxlen = sizeof(unsigned int),
73 .mode = 0644,
74 .proc_handler = sched_itmt_update_handler,
75 .extra1 = SYSCTL_ZERO,
76 .extra2 = SYSCTL_ONE,
77 },
78 {}
79 };
80
81 static struct ctl_table itmt_root_table[] = {
82 {
83 .procname = "kernel",
84 .mode = 0555,
85 .child = itmt_kern_table,
86 },
87 {}
88 };
89
90 static struct ctl_table_header *itmt_sysctl_header;
91
92 /**
93 * sched_set_itmt_support() - Indicate platform supports ITMT
94 *
95 * This function is used by the OS to indicate to scheduler that the platform
96 * is capable of supporting the ITMT feature.
97 *
98 * The current scheme has the pstate driver detects if the system
99 * is ITMT capable and call sched_set_itmt_support.
100 *
101 * This must be done only after sched_set_itmt_core_prio
102 * has been called to set the cpus' priorities.
103 * It must not be called with cpu hot plug lock
104 * held as we need to acquire the lock to rebuild sched domains
105 * later.
106 *
107 * Return: 0 on success
108 */
109 int sched_set_itmt_support(void)
110 {
111 mutex_lock(&itmt_update_mutex);
112
113 if (sched_itmt_capable) {
114 mutex_unlock(&itmt_update_mutex);
115 return 0;
116 }
117
118 itmt_sysctl_header = register_sysctl_table(itmt_root_table);
119 if (!itmt_sysctl_header) {
120 mutex_unlock(&itmt_update_mutex);
121 return -ENOMEM;
122 }
123
124 sched_itmt_capable = true;
125
126 sysctl_sched_itmt_enabled = 1;
127
128 x86_topology_update = true;
129 rebuild_sched_domains();
130
131 mutex_unlock(&itmt_update_mutex);
132
133 return 0;
134 }
135
136 /**
137 * sched_clear_itmt_support() - Revoke platform's support of ITMT
138 *
139 * This function is used by the OS to indicate that it has
140 * revoked the platform's support of ITMT feature.
141 *
142 * It must not be called with cpu hot plug lock
143 * held as we need to acquire the lock to rebuild sched domains
144 * later.
145 */
146 void sched_clear_itmt_support(void)
147 {
148 mutex_lock(&itmt_update_mutex);
149
150 if (!sched_itmt_capable) {
151 mutex_unlock(&itmt_update_mutex);
152 return;
153 }
154 sched_itmt_capable = false;
155
156 if (itmt_sysctl_header) {
157 unregister_sysctl_table(itmt_sysctl_header);
158 itmt_sysctl_header = NULL;
159 }
160
161 if (sysctl_sched_itmt_enabled) {
162 /* disable sched_itmt if we are no longer ITMT capable */
163 sysctl_sched_itmt_enabled = 0;
164 x86_topology_update = true;
165 rebuild_sched_domains();
166 }
167
168 mutex_unlock(&itmt_update_mutex);
169 }
170
171 int arch_asym_cpu_priority(int cpu)
172 {
173 return per_cpu(sched_core_priority, cpu);
174 }
175
176 /**
177 * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
178 * @prio: Priority of cpu core
179 * @core_cpu: The cpu number associated with the core
180 *
181 * The pstate driver will find out the max boost frequency
182 * and call this function to set a priority proportional
183 * to the max boost frequency. CPU with higher boost
184 * frequency will receive higher priority.
185 *
186 * No need to rebuild sched domain after updating
187 * the CPU priorities. The sched domains have no
188 * dependency on CPU priorities.
189 */
190 void sched_set_itmt_core_prio(int prio, int core_cpu)
191 {
192 int cpu, i = 1;
193
194 for_each_cpu(cpu, topology_sibling_cpumask(core_cpu)) {
195 int smt_prio;
196
197 /*
198 * Ensure that the siblings are moved to the end
199 * of the priority chain and only used when
200 * all other high priority cpus are out of capacity.
201 */
202 smt_prio = prio * smp_num_siblings / i;
203 per_cpu(sched_core_priority, cpu) = smt_prio;
204 i++;
205 }
206 }