Colin Cross | 4126c01 | 2012-05-07 17:57:41 -0700 | [diff] [blame] | 1 | /* |
| 2 | * coupled.c - helper functions to enter the same idle state on multiple cpus |
| 3 | * |
| 4 | * Copyright (c) 2011 Google, Inc. |
| 5 | * |
| 6 | * Author: Colin Cross <ccross@android.com> |
| 7 | * |
| 8 | * This program is free software; you can redistribute it and/or modify |
| 9 | * it under the terms of the GNU General Public License as published by |
| 10 | * the Free Software Foundation; either version 2 of the License, or |
| 11 | * (at your option) any later version. |
| 12 | * |
| 13 | * This program is distributed in the hope that it will be useful, but WITHOUT |
| 14 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 15 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
| 16 | * more details. |
| 17 | */ |
| 18 | |
| 19 | #include <linux/kernel.h> |
| 20 | #include <linux/cpu.h> |
| 21 | #include <linux/cpuidle.h> |
| 22 | #include <linux/mutex.h> |
| 23 | #include <linux/sched.h> |
| 24 | #include <linux/slab.h> |
| 25 | #include <linux/spinlock.h> |
| 26 | |
| 27 | #include "cpuidle.h" |
| 28 | |
| 29 | /** |
| 30 | * DOC: Coupled cpuidle states |
| 31 | * |
| 32 | * On some ARM SMP SoCs (OMAP4460, Tegra 2, and probably more), the |
| 33 | * cpus cannot be independently powered down, either due to |
| 34 | * sequencing restrictions (on Tegra 2, cpu 0 must be the last to |
| 35 | * power down), or due to HW bugs (on OMAP4460, a cpu powering up |
| 36 | * will corrupt the gic state unless the other cpu runs a work |
| 37 | * around). Each cpu has a power state that it can enter without |
| 38 | * coordinating with the other cpu (usually Wait For Interrupt, or |
| 39 | * WFI), and one or more "coupled" power states that affect blocks |
| 40 | * shared between the cpus (L2 cache, interrupt controller, and |
| 41 | * sometimes the whole SoC). Entering a coupled power state must |
| 42 | * be tightly controlled on both cpus. |
| 43 | * |
| 44 | * This file implements a solution, where each cpu will wait in the |
| 45 | * WFI state until all cpus are ready to enter a coupled state, at |
| 46 | * which point the coupled state function will be called on all |
| 47 | * cpus at approximately the same time. |
| 48 | * |
| 49 | * Once all cpus are ready to enter idle, they are woken by an smp |
| 50 | * cross call. At this point, there is a chance that one of the |
| 51 | * cpus will find work to do, and choose not to enter idle. A |
| 52 | * final pass is needed to guarantee that all cpus will call the |
| 53 | * power state enter function at the same time. During this pass, |
| 54 | * each cpu will increment the ready counter, and continue once the |
| 55 | * ready counter matches the number of online coupled cpus. If any |
| 56 | * cpu exits idle, the other cpus will decrement their counter and |
| 57 | * retry. |
| 58 | * |
| 59 | * requested_state stores the deepest coupled idle state each cpu |
| 60 | * is ready for. It is assumed that the states are indexed from |
| 61 | * shallowest (highest power, lowest exit latency) to deepest |
| 62 | * (lowest power, highest exit latency). The requested_state |
| 63 | * variable is not locked. It is only written from the cpu that |
| 64 | * it stores (or by the on/offlining cpu if that cpu is offline), |
| 65 | * and only read after all the cpus are ready for the coupled idle |
| 66 | * state are are no longer updating it. |
| 67 | * |
| 68 | * Three atomic counters are used. alive_count tracks the number |
| 69 | * of cpus in the coupled set that are currently or soon will be |
| 70 | * online. waiting_count tracks the number of cpus that are in |
| 71 | * the waiting loop, in the ready loop, or in the coupled idle state. |
| 72 | * ready_count tracks the number of cpus that are in the ready loop |
| 73 | * or in the coupled idle state. |
| 74 | * |
| 75 | * To use coupled cpuidle states, a cpuidle driver must: |
| 76 | * |
| 77 | * Set struct cpuidle_device.coupled_cpus to the mask of all |
| 78 | * coupled cpus, usually the same as cpu_possible_mask if all cpus |
| 79 | * are part of the same cluster. The coupled_cpus mask must be |
| 80 | * set in the struct cpuidle_device for each cpu. |
| 81 | * |
| 82 | * Set struct cpuidle_device.safe_state to a state that is not a |
| 83 | * coupled state. This is usually WFI. |
| 84 | * |
| 85 | * Set CPUIDLE_FLAG_COUPLED in struct cpuidle_state.flags for each |
| 86 | * state that affects multiple cpus. |
| 87 | * |
| 88 | * Provide a struct cpuidle_state.enter function for each state |
| 89 | * that affects multiple cpus. This function is guaranteed to be |
| 90 | * called on all cpus at approximately the same time. The driver |
| 91 | * should ensure that the cpus all abort together if any cpu tries |
| 92 | * to abort once the function is called. The function should return |
| 93 | * with interrupts still disabled. |
| 94 | */ |
| 95 | |
| 96 | /** |
| 97 | * struct cpuidle_coupled - data for set of cpus that share a coupled idle state |
| 98 | * @coupled_cpus: mask of cpus that are part of the coupled set |
| 99 | * @requested_state: array of requested states for cpus in the coupled set |
| 100 | * @ready_waiting_counts: combined count of cpus in ready or waiting loops |
| 101 | * @online_count: count of cpus that are online |
| 102 | * @refcnt: reference count of cpuidle devices that are using this struct |
| 103 | * @prevent: flag to prevent coupled idle while a cpu is hotplugging |
| 104 | */ |
| 105 | struct cpuidle_coupled { |
| 106 | cpumask_t coupled_cpus; |
| 107 | int requested_state[NR_CPUS]; |
| 108 | atomic_t ready_waiting_counts; |
| 109 | int online_count; |
| 110 | int refcnt; |
| 111 | int prevent; |
| 112 | }; |
| 113 | |
| 114 | #define WAITING_BITS 16 |
| 115 | #define MAX_WAITING_CPUS (1 << WAITING_BITS) |
| 116 | #define WAITING_MASK (MAX_WAITING_CPUS - 1) |
| 117 | #define READY_MASK (~WAITING_MASK) |
| 118 | |
| 119 | #define CPUIDLE_COUPLED_NOT_IDLE (-1) |
| 120 | |
| 121 | static DEFINE_MUTEX(cpuidle_coupled_lock); |
| 122 | static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb); |
| 123 | |
| 124 | /* |
| 125 | * The cpuidle_coupled_poked_mask mask is used to avoid calling |
| 126 | * __smp_call_function_single with the per cpu call_single_data struct already |
| 127 | * in use. This prevents a deadlock where two cpus are waiting for each others |
| 128 | * call_single_data struct to be available |
| 129 | */ |
| 130 | static cpumask_t cpuidle_coupled_poked_mask; |
| 131 | |
| 132 | /** |
Colin Cross | 20ff51a | 2012-05-07 17:57:42 -0700 | [diff] [blame] | 133 | * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus |
| 134 | * @dev: cpuidle_device of the calling cpu |
| 135 | * @a: atomic variable to hold the barrier |
| 136 | * |
| 137 | * No caller to this function will return from this function until all online |
| 138 | * cpus in the same coupled group have called this function. Once any caller |
| 139 | * has returned from this function, the barrier is immediately available for |
| 140 | * reuse. |
| 141 | * |
| 142 | * The atomic variable a must be initialized to 0 before any cpu calls |
| 143 | * this function, will be reset to 0 before any cpu returns from this function. |
| 144 | * |
| 145 | * Must only be called from within a coupled idle state handler |
| 146 | * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set). |
| 147 | * |
| 148 | * Provides full smp barrier semantics before and after calling. |
| 149 | */ |
| 150 | void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a) |
| 151 | { |
| 152 | int n = dev->coupled->online_count; |
| 153 | |
| 154 | smp_mb__before_atomic_inc(); |
| 155 | atomic_inc(a); |
| 156 | |
| 157 | while (atomic_read(a) < n) |
| 158 | cpu_relax(); |
| 159 | |
| 160 | if (atomic_inc_return(a) == n * 2) { |
| 161 | atomic_set(a, 0); |
| 162 | return; |
| 163 | } |
| 164 | |
| 165 | while (atomic_read(a) > n) |
| 166 | cpu_relax(); |
| 167 | } |
| 168 | |
| 169 | /** |
Colin Cross | 4126c01 | 2012-05-07 17:57:41 -0700 | [diff] [blame] | 170 | * cpuidle_state_is_coupled - check if a state is part of a coupled set |
| 171 | * @dev: struct cpuidle_device for the current cpu |
| 172 | * @drv: struct cpuidle_driver for the platform |
| 173 | * @state: index of the target state in drv->states |
| 174 | * |
| 175 | * Returns true if the target state is coupled with cpus besides this one |
| 176 | */ |
| 177 | bool cpuidle_state_is_coupled(struct cpuidle_device *dev, |
| 178 | struct cpuidle_driver *drv, int state) |
| 179 | { |
| 180 | return drv->states[state].flags & CPUIDLE_FLAG_COUPLED; |
| 181 | } |
| 182 | |
| 183 | /** |
| 184 | * cpuidle_coupled_set_ready - mark a cpu as ready |
| 185 | * @coupled: the struct coupled that contains the current cpu |
| 186 | */ |
| 187 | static inline void cpuidle_coupled_set_ready(struct cpuidle_coupled *coupled) |
| 188 | { |
| 189 | atomic_add(MAX_WAITING_CPUS, &coupled->ready_waiting_counts); |
| 190 | } |
| 191 | |
| 192 | /** |
| 193 | * cpuidle_coupled_set_not_ready - mark a cpu as not ready |
| 194 | * @coupled: the struct coupled that contains the current cpu |
| 195 | * |
| 196 | * Decrements the ready counter, unless the ready (and thus the waiting) counter |
| 197 | * is equal to the number of online cpus. Prevents a race where one cpu |
| 198 | * decrements the waiting counter and then re-increments it just before another |
| 199 | * cpu has decremented its ready counter, leading to the ready counter going |
| 200 | * down from the number of online cpus without going through the coupled idle |
| 201 | * state. |
| 202 | * |
| 203 | * Returns 0 if the counter was decremented successfully, -EINVAL if the ready |
| 204 | * counter was equal to the number of online cpus. |
| 205 | */ |
| 206 | static |
| 207 | inline int cpuidle_coupled_set_not_ready(struct cpuidle_coupled *coupled) |
| 208 | { |
| 209 | int all; |
| 210 | int ret; |
| 211 | |
| 212 | all = coupled->online_count || (coupled->online_count << WAITING_BITS); |
| 213 | ret = atomic_add_unless(&coupled->ready_waiting_counts, |
| 214 | -MAX_WAITING_CPUS, all); |
| 215 | |
| 216 | return ret ? 0 : -EINVAL; |
| 217 | } |
| 218 | |
| 219 | /** |
| 220 | * cpuidle_coupled_no_cpus_ready - check if no cpus in a coupled set are ready |
| 221 | * @coupled: the struct coupled that contains the current cpu |
| 222 | * |
| 223 | * Returns true if all of the cpus in a coupled set are out of the ready loop. |
| 224 | */ |
| 225 | static inline int cpuidle_coupled_no_cpus_ready(struct cpuidle_coupled *coupled) |
| 226 | { |
| 227 | int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS; |
| 228 | return r == 0; |
| 229 | } |
| 230 | |
| 231 | /** |
| 232 | * cpuidle_coupled_cpus_ready - check if all cpus in a coupled set are ready |
| 233 | * @coupled: the struct coupled that contains the current cpu |
| 234 | * |
| 235 | * Returns true if all cpus coupled to this target state are in the ready loop |
| 236 | */ |
| 237 | static inline bool cpuidle_coupled_cpus_ready(struct cpuidle_coupled *coupled) |
| 238 | { |
| 239 | int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS; |
| 240 | return r == coupled->online_count; |
| 241 | } |
| 242 | |
| 243 | /** |
| 244 | * cpuidle_coupled_cpus_waiting - check if all cpus in a coupled set are waiting |
| 245 | * @coupled: the struct coupled that contains the current cpu |
| 246 | * |
| 247 | * Returns true if all cpus coupled to this target state are in the wait loop |
| 248 | */ |
| 249 | static inline bool cpuidle_coupled_cpus_waiting(struct cpuidle_coupled *coupled) |
| 250 | { |
| 251 | int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK; |
| 252 | return w == coupled->online_count; |
| 253 | } |
| 254 | |
| 255 | /** |
| 256 | * cpuidle_coupled_no_cpus_waiting - check if no cpus in coupled set are waiting |
| 257 | * @coupled: the struct coupled that contains the current cpu |
| 258 | * |
| 259 | * Returns true if all of the cpus in a coupled set are out of the waiting loop. |
| 260 | */ |
| 261 | static inline int cpuidle_coupled_no_cpus_waiting(struct cpuidle_coupled *coupled) |
| 262 | { |
| 263 | int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK; |
| 264 | return w == 0; |
| 265 | } |
| 266 | |
| 267 | /** |
| 268 | * cpuidle_coupled_get_state - determine the deepest idle state |
| 269 | * @dev: struct cpuidle_device for this cpu |
| 270 | * @coupled: the struct coupled that contains the current cpu |
| 271 | * |
| 272 | * Returns the deepest idle state that all coupled cpus can enter |
| 273 | */ |
| 274 | static inline int cpuidle_coupled_get_state(struct cpuidle_device *dev, |
| 275 | struct cpuidle_coupled *coupled) |
| 276 | { |
| 277 | int i; |
| 278 | int state = INT_MAX; |
| 279 | |
| 280 | /* |
| 281 | * Read barrier ensures that read of requested_state is ordered after |
| 282 | * reads of ready_count. Matches the write barriers |
| 283 | * cpuidle_set_state_waiting. |
| 284 | */ |
| 285 | smp_rmb(); |
| 286 | |
| 287 | for_each_cpu_mask(i, coupled->coupled_cpus) |
| 288 | if (cpu_online(i) && coupled->requested_state[i] < state) |
| 289 | state = coupled->requested_state[i]; |
| 290 | |
| 291 | return state; |
| 292 | } |
| 293 | |
| 294 | static void cpuidle_coupled_poked(void *info) |
| 295 | { |
| 296 | int cpu = (unsigned long)info; |
| 297 | cpumask_clear_cpu(cpu, &cpuidle_coupled_poked_mask); |
| 298 | } |
| 299 | |
| 300 | /** |
| 301 | * cpuidle_coupled_poke - wake up a cpu that may be waiting |
| 302 | * @cpu: target cpu |
| 303 | * |
| 304 | * Ensures that the target cpu exits it's waiting idle state (if it is in it) |
| 305 | * and will see updates to waiting_count before it re-enters it's waiting idle |
| 306 | * state. |
| 307 | * |
| 308 | * If cpuidle_coupled_poked_mask is already set for the target cpu, that cpu |
| 309 | * either has or will soon have a pending IPI that will wake it out of idle, |
| 310 | * or it is currently processing the IPI and is not in idle. |
| 311 | */ |
| 312 | static void cpuidle_coupled_poke(int cpu) |
| 313 | { |
| 314 | struct call_single_data *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu); |
| 315 | |
| 316 | if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poked_mask)) |
| 317 | __smp_call_function_single(cpu, csd, 0); |
| 318 | } |
| 319 | |
| 320 | /** |
| 321 | * cpuidle_coupled_poke_others - wake up all other cpus that may be waiting |
| 322 | * @dev: struct cpuidle_device for this cpu |
| 323 | * @coupled: the struct coupled that contains the current cpu |
| 324 | * |
| 325 | * Calls cpuidle_coupled_poke on all other online cpus. |
| 326 | */ |
| 327 | static void cpuidle_coupled_poke_others(int this_cpu, |
| 328 | struct cpuidle_coupled *coupled) |
| 329 | { |
| 330 | int cpu; |
| 331 | |
| 332 | for_each_cpu_mask(cpu, coupled->coupled_cpus) |
| 333 | if (cpu != this_cpu && cpu_online(cpu)) |
| 334 | cpuidle_coupled_poke(cpu); |
| 335 | } |
| 336 | |
| 337 | /** |
| 338 | * cpuidle_coupled_set_waiting - mark this cpu as in the wait loop |
| 339 | * @dev: struct cpuidle_device for this cpu |
| 340 | * @coupled: the struct coupled that contains the current cpu |
| 341 | * @next_state: the index in drv->states of the requested state for this cpu |
| 342 | * |
| 343 | * Updates the requested idle state for the specified cpuidle device, |
| 344 | * poking all coupled cpus out of idle if necessary to let them see the new |
| 345 | * state. |
| 346 | */ |
| 347 | static void cpuidle_coupled_set_waiting(int cpu, |
| 348 | struct cpuidle_coupled *coupled, int next_state) |
| 349 | { |
| 350 | int w; |
| 351 | |
| 352 | coupled->requested_state[cpu] = next_state; |
| 353 | |
| 354 | /* |
| 355 | * If this is the last cpu to enter the waiting state, poke |
| 356 | * all the other cpus out of their waiting state so they can |
| 357 | * enter a deeper state. This can race with one of the cpus |
| 358 | * exiting the waiting state due to an interrupt and |
| 359 | * decrementing waiting_count, see comment below. |
| 360 | * |
| 361 | * The atomic_inc_return provides a write barrier to order the write |
| 362 | * to requested_state with the later write that increments ready_count. |
| 363 | */ |
| 364 | w = atomic_inc_return(&coupled->ready_waiting_counts) & WAITING_MASK; |
| 365 | if (w == coupled->online_count) |
| 366 | cpuidle_coupled_poke_others(cpu, coupled); |
| 367 | } |
| 368 | |
| 369 | /** |
| 370 | * cpuidle_coupled_set_not_waiting - mark this cpu as leaving the wait loop |
| 371 | * @dev: struct cpuidle_device for this cpu |
| 372 | * @coupled: the struct coupled that contains the current cpu |
| 373 | * |
| 374 | * Removes the requested idle state for the specified cpuidle device. |
| 375 | */ |
| 376 | static void cpuidle_coupled_set_not_waiting(int cpu, |
| 377 | struct cpuidle_coupled *coupled) |
| 378 | { |
| 379 | /* |
| 380 | * Decrementing waiting count can race with incrementing it in |
| 381 | * cpuidle_coupled_set_waiting, but that's OK. Worst case, some |
| 382 | * cpus will increment ready_count and then spin until they |
| 383 | * notice that this cpu has cleared it's requested_state. |
| 384 | */ |
| 385 | atomic_dec(&coupled->ready_waiting_counts); |
| 386 | |
| 387 | coupled->requested_state[cpu] = CPUIDLE_COUPLED_NOT_IDLE; |
| 388 | } |
| 389 | |
| 390 | /** |
| 391 | * cpuidle_coupled_set_done - mark this cpu as leaving the ready loop |
| 392 | * @cpu: the current cpu |
| 393 | * @coupled: the struct coupled that contains the current cpu |
| 394 | * |
| 395 | * Marks this cpu as no longer in the ready and waiting loops. Decrements |
| 396 | * the waiting count first to prevent another cpu looping back in and seeing |
| 397 | * this cpu as waiting just before it exits idle. |
| 398 | */ |
| 399 | static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled) |
| 400 | { |
| 401 | cpuidle_coupled_set_not_waiting(cpu, coupled); |
| 402 | atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts); |
| 403 | } |
| 404 | |
| 405 | /** |
| 406 | * cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed |
| 407 | * @cpu - this cpu |
| 408 | * |
| 409 | * Turns on interrupts and spins until any outstanding poke interrupts have |
| 410 | * been processed and the poke bit has been cleared. |
| 411 | * |
| 412 | * Other interrupts may also be processed while interrupts are enabled, so |
| 413 | * need_resched() must be tested after turning interrupts off again to make sure |
| 414 | * the interrupt didn't schedule work that should take the cpu out of idle. |
| 415 | * |
| 416 | * Returns 0 if need_resched was false, -EINTR if need_resched was true. |
| 417 | */ |
| 418 | static int cpuidle_coupled_clear_pokes(int cpu) |
| 419 | { |
| 420 | local_irq_enable(); |
| 421 | while (cpumask_test_cpu(cpu, &cpuidle_coupled_poked_mask)) |
| 422 | cpu_relax(); |
| 423 | local_irq_disable(); |
| 424 | |
| 425 | return need_resched() ? -EINTR : 0; |
| 426 | } |
| 427 | |
| 428 | /** |
| 429 | * cpuidle_enter_state_coupled - attempt to enter a state with coupled cpus |
| 430 | * @dev: struct cpuidle_device for the current cpu |
| 431 | * @drv: struct cpuidle_driver for the platform |
| 432 | * @next_state: index of the requested state in drv->states |
| 433 | * |
| 434 | * Coordinate with coupled cpus to enter the target state. This is a two |
| 435 | * stage process. In the first stage, the cpus are operating independently, |
| 436 | * and may call into cpuidle_enter_state_coupled at completely different times. |
| 437 | * To save as much power as possible, the first cpus to call this function will |
| 438 | * go to an intermediate state (the cpuidle_device's safe state), and wait for |
| 439 | * all the other cpus to call this function. Once all coupled cpus are idle, |
| 440 | * the second stage will start. Each coupled cpu will spin until all cpus have |
| 441 | * guaranteed that they will call the target_state. |
| 442 | * |
| 443 | * This function must be called with interrupts disabled. It may enable |
| 444 | * interrupts while preparing for idle, and it will always return with |
| 445 | * interrupts enabled. |
| 446 | */ |
| 447 | int cpuidle_enter_state_coupled(struct cpuidle_device *dev, |
| 448 | struct cpuidle_driver *drv, int next_state) |
| 449 | { |
| 450 | int entered_state = -1; |
| 451 | struct cpuidle_coupled *coupled = dev->coupled; |
| 452 | |
| 453 | if (!coupled) |
| 454 | return -EINVAL; |
| 455 | |
| 456 | while (coupled->prevent) { |
| 457 | if (cpuidle_coupled_clear_pokes(dev->cpu)) { |
| 458 | local_irq_enable(); |
| 459 | return entered_state; |
| 460 | } |
| 461 | entered_state = cpuidle_enter_state(dev, drv, |
| 462 | dev->safe_state_index); |
| 463 | } |
| 464 | |
| 465 | /* Read barrier ensures online_count is read after prevent is cleared */ |
| 466 | smp_rmb(); |
| 467 | |
| 468 | cpuidle_coupled_set_waiting(dev->cpu, coupled, next_state); |
| 469 | |
| 470 | retry: |
| 471 | /* |
| 472 | * Wait for all coupled cpus to be idle, using the deepest state |
| 473 | * allowed for a single cpu. |
| 474 | */ |
| 475 | while (!cpuidle_coupled_cpus_waiting(coupled)) { |
| 476 | if (cpuidle_coupled_clear_pokes(dev->cpu)) { |
| 477 | cpuidle_coupled_set_not_waiting(dev->cpu, coupled); |
| 478 | goto out; |
| 479 | } |
| 480 | |
| 481 | if (coupled->prevent) { |
| 482 | cpuidle_coupled_set_not_waiting(dev->cpu, coupled); |
| 483 | goto out; |
| 484 | } |
| 485 | |
| 486 | entered_state = cpuidle_enter_state(dev, drv, |
| 487 | dev->safe_state_index); |
| 488 | } |
| 489 | |
| 490 | if (cpuidle_coupled_clear_pokes(dev->cpu)) { |
| 491 | cpuidle_coupled_set_not_waiting(dev->cpu, coupled); |
| 492 | goto out; |
| 493 | } |
| 494 | |
| 495 | /* |
| 496 | * All coupled cpus are probably idle. There is a small chance that |
| 497 | * one of the other cpus just became active. Increment the ready count, |
| 498 | * and spin until all coupled cpus have incremented the counter. Once a |
| 499 | * cpu has incremented the ready counter, it cannot abort idle and must |
| 500 | * spin until either all cpus have incremented the ready counter, or |
| 501 | * another cpu leaves idle and decrements the waiting counter. |
| 502 | */ |
| 503 | |
| 504 | cpuidle_coupled_set_ready(coupled); |
| 505 | while (!cpuidle_coupled_cpus_ready(coupled)) { |
| 506 | /* Check if any other cpus bailed out of idle. */ |
| 507 | if (!cpuidle_coupled_cpus_waiting(coupled)) |
| 508 | if (!cpuidle_coupled_set_not_ready(coupled)) |
| 509 | goto retry; |
| 510 | |
| 511 | cpu_relax(); |
| 512 | } |
| 513 | |
| 514 | /* all cpus have acked the coupled state */ |
| 515 | next_state = cpuidle_coupled_get_state(dev, coupled); |
| 516 | |
| 517 | entered_state = cpuidle_enter_state(dev, drv, next_state); |
| 518 | |
| 519 | cpuidle_coupled_set_done(dev->cpu, coupled); |
| 520 | |
| 521 | out: |
| 522 | /* |
| 523 | * Normal cpuidle states are expected to return with irqs enabled. |
| 524 | * That leads to an inefficiency where a cpu receiving an interrupt |
| 525 | * that brings it out of idle will process that interrupt before |
| 526 | * exiting the idle enter function and decrementing ready_count. All |
| 527 | * other cpus will need to spin waiting for the cpu that is processing |
| 528 | * the interrupt. If the driver returns with interrupts disabled, |
| 529 | * all other cpus will loop back into the safe idle state instead of |
| 530 | * spinning, saving power. |
| 531 | * |
| 532 | * Calling local_irq_enable here allows coupled states to return with |
| 533 | * interrupts disabled, but won't cause problems for drivers that |
| 534 | * exit with interrupts enabled. |
| 535 | */ |
| 536 | local_irq_enable(); |
| 537 | |
| 538 | /* |
| 539 | * Wait until all coupled cpus have exited idle. There is no risk that |
| 540 | * a cpu exits and re-enters the ready state because this cpu has |
| 541 | * already decremented its waiting_count. |
| 542 | */ |
| 543 | while (!cpuidle_coupled_no_cpus_ready(coupled)) |
| 544 | cpu_relax(); |
| 545 | |
| 546 | return entered_state; |
| 547 | } |
| 548 | |
| 549 | static void cpuidle_coupled_update_online_cpus(struct cpuidle_coupled *coupled) |
| 550 | { |
| 551 | cpumask_t cpus; |
| 552 | cpumask_and(&cpus, cpu_online_mask, &coupled->coupled_cpus); |
| 553 | coupled->online_count = cpumask_weight(&cpus); |
| 554 | } |
| 555 | |
| 556 | /** |
| 557 | * cpuidle_coupled_register_device - register a coupled cpuidle device |
| 558 | * @dev: struct cpuidle_device for the current cpu |
| 559 | * |
| 560 | * Called from cpuidle_register_device to handle coupled idle init. Finds the |
| 561 | * cpuidle_coupled struct for this set of coupled cpus, or creates one if none |
| 562 | * exists yet. |
| 563 | */ |
| 564 | int cpuidle_coupled_register_device(struct cpuidle_device *dev) |
| 565 | { |
| 566 | int cpu; |
| 567 | struct cpuidle_device *other_dev; |
| 568 | struct call_single_data *csd; |
| 569 | struct cpuidle_coupled *coupled; |
| 570 | |
| 571 | if (cpumask_empty(&dev->coupled_cpus)) |
| 572 | return 0; |
| 573 | |
| 574 | for_each_cpu_mask(cpu, dev->coupled_cpus) { |
| 575 | other_dev = per_cpu(cpuidle_devices, cpu); |
| 576 | if (other_dev && other_dev->coupled) { |
| 577 | coupled = other_dev->coupled; |
| 578 | goto have_coupled; |
| 579 | } |
| 580 | } |
| 581 | |
| 582 | /* No existing coupled info found, create a new one */ |
| 583 | coupled = kzalloc(sizeof(struct cpuidle_coupled), GFP_KERNEL); |
| 584 | if (!coupled) |
| 585 | return -ENOMEM; |
| 586 | |
| 587 | coupled->coupled_cpus = dev->coupled_cpus; |
| 588 | |
| 589 | have_coupled: |
| 590 | dev->coupled = coupled; |
| 591 | if (WARN_ON(!cpumask_equal(&dev->coupled_cpus, &coupled->coupled_cpus))) |
| 592 | coupled->prevent++; |
| 593 | |
| 594 | cpuidle_coupled_update_online_cpus(coupled); |
| 595 | |
| 596 | coupled->refcnt++; |
| 597 | |
| 598 | csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu); |
| 599 | csd->func = cpuidle_coupled_poked; |
| 600 | csd->info = (void *)(unsigned long)dev->cpu; |
| 601 | |
| 602 | return 0; |
| 603 | } |
| 604 | |
| 605 | /** |
| 606 | * cpuidle_coupled_unregister_device - unregister a coupled cpuidle device |
| 607 | * @dev: struct cpuidle_device for the current cpu |
| 608 | * |
| 609 | * Called from cpuidle_unregister_device to tear down coupled idle. Removes the |
| 610 | * cpu from the coupled idle set, and frees the cpuidle_coupled_info struct if |
| 611 | * this was the last cpu in the set. |
| 612 | */ |
| 613 | void cpuidle_coupled_unregister_device(struct cpuidle_device *dev) |
| 614 | { |
| 615 | struct cpuidle_coupled *coupled = dev->coupled; |
| 616 | |
| 617 | if (cpumask_empty(&dev->coupled_cpus)) |
| 618 | return; |
| 619 | |
| 620 | if (--coupled->refcnt) |
| 621 | kfree(coupled); |
| 622 | dev->coupled = NULL; |
| 623 | } |
| 624 | |
| 625 | /** |
| 626 | * cpuidle_coupled_prevent_idle - prevent cpus from entering a coupled state |
| 627 | * @coupled: the struct coupled that contains the cpu that is changing state |
| 628 | * |
| 629 | * Disables coupled cpuidle on a coupled set of cpus. Used to ensure that |
| 630 | * cpu_online_mask doesn't change while cpus are coordinating coupled idle. |
| 631 | */ |
| 632 | static void cpuidle_coupled_prevent_idle(struct cpuidle_coupled *coupled) |
| 633 | { |
| 634 | int cpu = get_cpu(); |
| 635 | |
| 636 | /* Force all cpus out of the waiting loop. */ |
| 637 | coupled->prevent++; |
| 638 | cpuidle_coupled_poke_others(cpu, coupled); |
| 639 | put_cpu(); |
| 640 | while (!cpuidle_coupled_no_cpus_waiting(coupled)) |
| 641 | cpu_relax(); |
| 642 | } |
| 643 | |
| 644 | /** |
| 645 | * cpuidle_coupled_allow_idle - allows cpus to enter a coupled state |
| 646 | * @coupled: the struct coupled that contains the cpu that is changing state |
| 647 | * |
| 648 | * Enables coupled cpuidle on a coupled set of cpus. Used to ensure that |
| 649 | * cpu_online_mask doesn't change while cpus are coordinating coupled idle. |
| 650 | */ |
| 651 | static void cpuidle_coupled_allow_idle(struct cpuidle_coupled *coupled) |
| 652 | { |
| 653 | int cpu = get_cpu(); |
| 654 | |
| 655 | /* |
| 656 | * Write barrier ensures readers see the new online_count when they |
| 657 | * see prevent == 0. |
| 658 | */ |
| 659 | smp_wmb(); |
| 660 | coupled->prevent--; |
| 661 | /* Force cpus out of the prevent loop. */ |
| 662 | cpuidle_coupled_poke_others(cpu, coupled); |
| 663 | put_cpu(); |
| 664 | } |
| 665 | |
| 666 | /** |
| 667 | * cpuidle_coupled_cpu_notify - notifier called during hotplug transitions |
| 668 | * @nb: notifier block |
| 669 | * @action: hotplug transition |
| 670 | * @hcpu: target cpu number |
| 671 | * |
| 672 | * Called when a cpu is brought on or offline using hotplug. Updates the |
| 673 | * coupled cpu set appropriately |
| 674 | */ |
| 675 | static int cpuidle_coupled_cpu_notify(struct notifier_block *nb, |
| 676 | unsigned long action, void *hcpu) |
| 677 | { |
| 678 | int cpu = (unsigned long)hcpu; |
| 679 | struct cpuidle_device *dev; |
| 680 | |
Colin Cross | 63c6ba4 | 2012-08-15 22:10:50 +0200 | [diff] [blame^] | 681 | switch (action & ~CPU_TASKS_FROZEN) { |
| 682 | case CPU_UP_PREPARE: |
| 683 | case CPU_DOWN_PREPARE: |
| 684 | case CPU_ONLINE: |
| 685 | case CPU_DEAD: |
| 686 | case CPU_UP_CANCELED: |
| 687 | case CPU_DOWN_FAILED: |
| 688 | break; |
| 689 | default: |
| 690 | return NOTIFY_OK; |
| 691 | } |
| 692 | |
Colin Cross | 4126c01 | 2012-05-07 17:57:41 -0700 | [diff] [blame] | 693 | mutex_lock(&cpuidle_lock); |
| 694 | |
| 695 | dev = per_cpu(cpuidle_devices, cpu); |
| 696 | if (!dev->coupled) |
| 697 | goto out; |
| 698 | |
| 699 | switch (action & ~CPU_TASKS_FROZEN) { |
| 700 | case CPU_UP_PREPARE: |
| 701 | case CPU_DOWN_PREPARE: |
| 702 | cpuidle_coupled_prevent_idle(dev->coupled); |
| 703 | break; |
| 704 | case CPU_ONLINE: |
| 705 | case CPU_DEAD: |
| 706 | cpuidle_coupled_update_online_cpus(dev->coupled); |
| 707 | /* Fall through */ |
| 708 | case CPU_UP_CANCELED: |
| 709 | case CPU_DOWN_FAILED: |
| 710 | cpuidle_coupled_allow_idle(dev->coupled); |
| 711 | break; |
| 712 | } |
| 713 | |
| 714 | out: |
| 715 | mutex_unlock(&cpuidle_lock); |
| 716 | return NOTIFY_OK; |
| 717 | } |
| 718 | |
| 719 | static struct notifier_block cpuidle_coupled_cpu_notifier = { |
| 720 | .notifier_call = cpuidle_coupled_cpu_notify, |
| 721 | }; |
| 722 | |
| 723 | static int __init cpuidle_coupled_init(void) |
| 724 | { |
| 725 | return register_cpu_notifier(&cpuidle_coupled_cpu_notifier); |
| 726 | } |
| 727 | core_initcall(cpuidle_coupled_init); |