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