1 /* 2 * Generic entry point for the idle threads 3 */ 4 #include <linux/sched.h> 5 #include <linux/cpu.h> 6 #include <linux/cpuidle.h> 7 #include <linux/tick.h> 8 #include <linux/mm.h> 9 #include <linux/stackprotector.h> 10 11 #include <asm/tlb.h> 12 13 #include <trace/events/power.h> 14 15 #include "sched.h" 16 17 static int __read_mostly cpu_idle_force_poll; 18 19 void cpu_idle_poll_ctrl(bool enable) 20 { 21 if (enable) { 22 cpu_idle_force_poll++; 23 } else { 24 cpu_idle_force_poll--; 25 WARN_ON_ONCE(cpu_idle_force_poll < 0); 26 } 27 } 28 29 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP 30 static int __init cpu_idle_poll_setup(char *__unused) 31 { 32 cpu_idle_force_poll = 1; 33 return 1; 34 } 35 __setup("nohlt", cpu_idle_poll_setup); 36 37 static int __init cpu_idle_nopoll_setup(char *__unused) 38 { 39 cpu_idle_force_poll = 0; 40 return 1; 41 } 42 __setup("hlt", cpu_idle_nopoll_setup); 43 #endif 44 45 static inline int cpu_idle_poll(void) 46 { 47 rcu_idle_enter(); 48 trace_cpu_idle_rcuidle(0, smp_processor_id()); 49 local_irq_enable(); 50 while (!tif_need_resched() && 51 (cpu_idle_force_poll || tick_check_broadcast_expired())) 52 cpu_relax(); 53 trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id()); 54 rcu_idle_exit(); 55 return 1; 56 } 57 58 /* Weak implementations for optional arch specific functions */ 59 void __weak arch_cpu_idle_prepare(void) { } 60 void __weak arch_cpu_idle_enter(void) { } 61 void __weak arch_cpu_idle_exit(void) { } 62 void __weak arch_cpu_idle_dead(void) { } 63 void __weak arch_cpu_idle(void) 64 { 65 cpu_idle_force_poll = 1; 66 local_irq_enable(); 67 } 68 69 /** 70 * cpuidle_idle_call - the main idle function 71 * 72 * NOTE: no locks or semaphores should be used here 73 * 74 * On archs that support TIF_POLLING_NRFLAG, is called with polling 75 * set, and it returns with polling set. If it ever stops polling, it 76 * must clear the polling bit. 77 */ 78 static void cpuidle_idle_call(void) 79 { 80 struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices); 81 struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); 82 int next_state, entered_state; 83 unsigned int broadcast; 84 85 /* 86 * Check if the idle task must be rescheduled. If it is the 87 * case, exit the function after re-enabling the local irq. 88 */ 89 if (need_resched()) { 90 local_irq_enable(); 91 return; 92 } 93 94 /* 95 * During the idle period, stop measuring the disabled irqs 96 * critical sections latencies 97 */ 98 stop_critical_timings(); 99 100 /* 101 * Tell the RCU framework we are entering an idle section, 102 * so no more rcu read side critical sections and one more 103 * step to the grace period 104 */ 105 rcu_idle_enter(); 106 107 /* 108 * Ask the cpuidle framework to choose a convenient idle state. 109 * Fall back to the default arch idle method on errors. 110 */ 111 next_state = cpuidle_select(drv, dev); 112 if (next_state < 0) { 113 use_default: 114 /* 115 * We can't use the cpuidle framework, let's use the default 116 * idle routine. 117 */ 118 if (current_clr_polling_and_test()) 119 local_irq_enable(); 120 else 121 arch_cpu_idle(); 122 123 goto exit_idle; 124 } 125 126 127 /* 128 * The idle task must be scheduled, it is pointless to 129 * go to idle, just update no idle residency and get 130 * out of this function 131 */ 132 if (current_clr_polling_and_test()) { 133 dev->last_residency = 0; 134 entered_state = next_state; 135 local_irq_enable(); 136 goto exit_idle; 137 } 138 139 broadcast = drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP; 140 141 /* 142 * Tell the time framework to switch to a broadcast timer 143 * because our local timer will be shutdown. If a local timer 144 * is used from another cpu as a broadcast timer, this call may 145 * fail if it is not available 146 */ 147 if (broadcast && 148 clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu)) 149 goto use_default; 150 151 /* Take note of the planned idle state. */ 152 idle_set_state(this_rq(), &drv->states[next_state]); 153 154 /* 155 * Enter the idle state previously returned by the governor decision. 156 * This function will block until an interrupt occurs and will take 157 * care of re-enabling the local interrupts 158 */ 159 entered_state = cpuidle_enter(drv, dev, next_state); 160 161 /* The cpu is no longer idle or about to enter idle. */ 162 idle_set_state(this_rq(), NULL); 163 164 if (broadcast) 165 clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu); 166 167 /* 168 * Give the governor an opportunity to reflect on the outcome 169 */ 170 cpuidle_reflect(dev, entered_state); 171 172 exit_idle: 173 __current_set_polling(); 174 175 /* 176 * It is up to the idle functions to reenable local interrupts 177 */ 178 if (WARN_ON_ONCE(irqs_disabled())) 179 local_irq_enable(); 180 181 rcu_idle_exit(); 182 start_critical_timings(); 183 } 184 185 /* 186 * Generic idle loop implementation 187 * 188 * Called with polling cleared. 189 */ 190 static void cpu_idle_loop(void) 191 { 192 while (1) { 193 /* 194 * If the arch has a polling bit, we maintain an invariant: 195 * 196 * Our polling bit is clear if we're not scheduled (i.e. if 197 * rq->curr != rq->idle). This means that, if rq->idle has 198 * the polling bit set, then setting need_resched is 199 * guaranteed to cause the cpu to reschedule. 200 */ 201 202 __current_set_polling(); 203 tick_nohz_idle_enter(); 204 205 while (!need_resched()) { 206 check_pgt_cache(); 207 rmb(); 208 209 if (cpu_is_offline(smp_processor_id())) 210 arch_cpu_idle_dead(); 211 212 local_irq_disable(); 213 arch_cpu_idle_enter(); 214 215 /* 216 * In poll mode we reenable interrupts and spin. 217 * 218 * Also if we detected in the wakeup from idle 219 * path that the tick broadcast device expired 220 * for us, we don't want to go deep idle as we 221 * know that the IPI is going to arrive right 222 * away 223 */ 224 if (cpu_idle_force_poll || tick_check_broadcast_expired()) 225 cpu_idle_poll(); 226 else 227 cpuidle_idle_call(); 228 229 arch_cpu_idle_exit(); 230 } 231 232 /* 233 * Since we fell out of the loop above, we know 234 * TIF_NEED_RESCHED must be set, propagate it into 235 * PREEMPT_NEED_RESCHED. 236 * 237 * This is required because for polling idle loops we will 238 * not have had an IPI to fold the state for us. 239 */ 240 preempt_set_need_resched(); 241 tick_nohz_idle_exit(); 242 __current_clr_polling(); 243 244 /* 245 * We promise to call sched_ttwu_pending and reschedule 246 * if need_resched is set while polling is set. That 247 * means that clearing polling needs to be visible 248 * before doing these things. 249 */ 250 smp_mb__after_atomic(); 251 252 sched_ttwu_pending(); 253 schedule_preempt_disabled(); 254 } 255 } 256 257 void cpu_startup_entry(enum cpuhp_state state) 258 { 259 /* 260 * This #ifdef needs to die, but it's too late in the cycle to 261 * make this generic (arm and sh have never invoked the canary 262 * init for the non boot cpus!). Will be fixed in 3.11 263 */ 264 #ifdef CONFIG_X86 265 /* 266 * If we're the non-boot CPU, nothing set the stack canary up 267 * for us. The boot CPU already has it initialized but no harm 268 * in doing it again. This is a good place for updating it, as 269 * we wont ever return from this function (so the invalid 270 * canaries already on the stack wont ever trigger). 271 */ 272 boot_init_stack_canary(); 273 #endif 274 arch_cpu_idle_prepare(); 275 cpu_idle_loop(); 276 } 277