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Linux/arch/x86/kernel/itmt.c

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  1 /*
  2  * itmt.c: Support Intel Turbo Boost Max Technology 3.0
  3  *
  4  * (C) Copyright 2016 Intel Corporation
  5  * Author: Tim Chen <tim.c.chen@linux.intel.com>
  6  *
  7  * This program is free software; you can redistribute it and/or
  8  * modify it under the terms of the GNU General Public License
  9  * as published by the Free Software Foundation; version 2
 10  * of the License.
 11  *
 12  * On platforms supporting Intel Turbo Boost Max Technology 3.0, (ITMT),
 13  * the maximum turbo frequencies of some cores in a CPU package may be
 14  * higher than for the other cores in the same package.  In that case,
 15  * better performance can be achieved by making the scheduler prefer
 16  * to run tasks on the CPUs with higher max turbo frequencies.
 17  *
 18  * This file provides functions and data structures for enabling the
 19  * scheduler to favor scheduling on cores can be boosted to a higher
 20  * frequency under ITMT.
 21  */
 22 
 23 #include <linux/sched.h>
 24 #include <linux/cpumask.h>
 25 #include <linux/cpuset.h>
 26 #include <linux/mutex.h>
 27 #include <linux/sched.h>
 28 #include <linux/sysctl.h>
 29 #include <linux/nodemask.h>
 30 
 31 static DEFINE_MUTEX(itmt_update_mutex);
 32 DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);
 33 
 34 /* Boolean to track if system has ITMT capabilities */
 35 static bool __read_mostly sched_itmt_capable;
 36 
 37 /*
 38  * Boolean to control whether we want to move processes to cpu capable
 39  * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
 40  * Technology 3.0.
 41  *
 42  * It can be set via /proc/sys/kernel/sched_itmt_enabled
 43  */
 44 unsigned int __read_mostly sysctl_sched_itmt_enabled;
 45 
 46 static int sched_itmt_update_handler(struct ctl_table *table, int write,
 47                                      void __user *buffer, size_t *lenp,
 48                                      loff_t *ppos)
 49 {
 50         unsigned int old_sysctl;
 51         int ret;
 52 
 53         mutex_lock(&itmt_update_mutex);
 54 
 55         if (!sched_itmt_capable) {
 56                 mutex_unlock(&itmt_update_mutex);
 57                 return -EINVAL;
 58         }
 59 
 60         old_sysctl = sysctl_sched_itmt_enabled;
 61         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 62 
 63         if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
 64                 x86_topology_update = true;
 65                 rebuild_sched_domains();
 66         }
 67 
 68         mutex_unlock(&itmt_update_mutex);
 69 
 70         return ret;
 71 }
 72 
 73 static unsigned int zero;
 74 static unsigned int one = 1;
 75 static struct ctl_table itmt_kern_table[] = {
 76         {
 77                 .procname       = "sched_itmt_enabled",
 78                 .data           = &sysctl_sched_itmt_enabled,
 79                 .maxlen         = sizeof(unsigned int),
 80                 .mode           = 0644,
 81                 .proc_handler   = sched_itmt_update_handler,
 82                 .extra1         = &zero,
 83                 .extra2         = &one,
 84         },
 85         {}
 86 };
 87 
 88 static struct ctl_table itmt_root_table[] = {
 89         {
 90                 .procname       = "kernel",
 91                 .mode           = 0555,
 92                 .child          = itmt_kern_table,
 93         },
 94         {}
 95 };
 96 
 97 static struct ctl_table_header *itmt_sysctl_header;
 98 
 99 /**
100  * sched_set_itmt_support() - Indicate platform supports ITMT
101  *
102  * This function is used by the OS to indicate to scheduler that the platform
103  * is capable of supporting the ITMT feature.
104  *
105  * The current scheme has the pstate driver detects if the system
106  * is ITMT capable and call sched_set_itmt_support.
107  *
108  * This must be done only after sched_set_itmt_core_prio
109  * has been called to set the cpus' priorities.
110  * It must not be called with cpu hot plug lock
111  * held as we need to acquire the lock to rebuild sched domains
112  * later.
113  *
114  * Return: 0 on success
115  */
116 int sched_set_itmt_support(void)
117 {
118         mutex_lock(&itmt_update_mutex);
119 
120         if (sched_itmt_capable) {
121                 mutex_unlock(&itmt_update_mutex);
122                 return 0;
123         }
124 
125         itmt_sysctl_header = register_sysctl_table(itmt_root_table);
126         if (!itmt_sysctl_header) {
127                 mutex_unlock(&itmt_update_mutex);
128                 return -ENOMEM;
129         }
130 
131         sched_itmt_capable = true;
132 
133         sysctl_sched_itmt_enabled = 1;
134 
135         x86_topology_update = true;
136         rebuild_sched_domains();
137 
138         mutex_unlock(&itmt_update_mutex);
139 
140         return 0;
141 }
142 
143 /**
144  * sched_clear_itmt_support() - Revoke platform's support of ITMT
145  *
146  * This function is used by the OS to indicate that it has
147  * revoked the platform's support of ITMT feature.
148  *
149  * It must not be called with cpu hot plug lock
150  * held as we need to acquire the lock to rebuild sched domains
151  * later.
152  */
153 void sched_clear_itmt_support(void)
154 {
155         mutex_lock(&itmt_update_mutex);
156 
157         if (!sched_itmt_capable) {
158                 mutex_unlock(&itmt_update_mutex);
159                 return;
160         }
161         sched_itmt_capable = false;
162 
163         if (itmt_sysctl_header) {
164                 unregister_sysctl_table(itmt_sysctl_header);
165                 itmt_sysctl_header = NULL;
166         }
167 
168         if (sysctl_sched_itmt_enabled) {
169                 /* disable sched_itmt if we are no longer ITMT capable */
170                 sysctl_sched_itmt_enabled = 0;
171                 x86_topology_update = true;
172                 rebuild_sched_domains();
173         }
174 
175         mutex_unlock(&itmt_update_mutex);
176 }
177 
178 int arch_asym_cpu_priority(int cpu)
179 {
180         return per_cpu(sched_core_priority, cpu);
181 }
182 
183 /**
184  * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
185  * @prio:       Priority of cpu core
186  * @core_cpu:   The cpu number associated with the core
187  *
188  * The pstate driver will find out the max boost frequency
189  * and call this function to set a priority proportional
190  * to the max boost frequency. CPU with higher boost
191  * frequency will receive higher priority.
192  *
193  * No need to rebuild sched domain after updating
194  * the CPU priorities. The sched domains have no
195  * dependency on CPU priorities.
196  */
197 void sched_set_itmt_core_prio(int prio, int core_cpu)
198 {
199         int cpu, i = 1;
200 
201         for_each_cpu(cpu, topology_sibling_cpumask(core_cpu)) {
202                 int smt_prio;
203 
204                 /*
205                  * Ensure that the siblings are moved to the end
206                  * of the priority chain and only used when
207                  * all other high priority cpus are out of capacity.
208                  */
209                 smt_prio = prio * smp_num_siblings / i;
210                 per_cpu(sched_core_priority, cpu) = smt_prio;
211                 i++;
212         }
213 }
214 

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