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