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Message-ID: <20180812221338.vwyorgitaqxkbldg@mwanda>
Date: Mon, 13 Aug 2018 01:13:38 +0300
From: Dan Carpenter <dan.carpenter@...cle.com>
To: kbuild@...org, "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: kbuild-all@...org, Linux PM <linux-pm@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Leo Yan <leo.yan@...aro.org>,
Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH] cpuidle: menu: Handle stopped tick more aggressively
Hi Rafael,
I love your patch! Perhaps something to improve:
url: https://github.com/0day-ci/linux/commits/Rafael-J-Wysocki/cpuidle-menu-Handle-stopped-tick-more-aggressively/20180811-191914
base: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
smatch warnings:
drivers/cpuidle/governors/menu.c:374 menu_select() error: uninitialized symbol 'first_idx'.
# https://github.com/0day-ci/linux/commit/5f9f09809ebd1b4f7820c9925a0cbd417bd3a823
git remote add linux-review https://github.com/0day-ci/linux
git remote update linux-review
git checkout 5f9f09809ebd1b4f7820c9925a0cbd417bd3a823
vim +/first_idx +374 drivers/cpuidle/governors/menu.c
1f85f87d4 Arjan van de Ven 2010-05-24 276
4f86d3a8e Len Brown 2007-10-03 277 /**
4f86d3a8e Len Brown 2007-10-03 278 * menu_select - selects the next idle state to enter
46bcfad7a Deepthi Dharwar 2011-10-28 279 * @drv: cpuidle driver containing state data
4f86d3a8e Len Brown 2007-10-03 280 * @dev: the CPU
45f1ff59e Rafael J. Wysocki 2018-03-22 281 * @stop_tick: indication on whether or not to stop the tick
4f86d3a8e Len Brown 2007-10-03 282 */
45f1ff59e Rafael J. Wysocki 2018-03-22 283 static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
45f1ff59e Rafael J. Wysocki 2018-03-22 284 bool *stop_tick)
4f86d3a8e Len Brown 2007-10-03 285 {
229b6863b Christoph Lameter 2014-08-17 286 struct menu_device *data = this_cpu_ptr(&menu_devices);
0fc784fb0 Rafael J. Wysocki 2018-05-30 287 int latency_req = cpuidle_governor_latency_req(dev->cpu);
4f86d3a8e Len Brown 2007-10-03 288 int i;
3ed09c945 Nicholas Piggin 2017-06-26 289 int first_idx;
3ed09c945 Nicholas Piggin 2017-06-26 290 int idx;
96e95182e tuukka.tikkanen@...aro.org 2014-02-24 291 unsigned int interactivity_req;
e132b9b3b Rik van Riel 2016-03-16 292 unsigned int expected_interval;
372ba8cb4 Mel Gorman 2014-08-06 293 unsigned long nr_iowaiters, cpu_load;
296bb1e51 Rafael J. Wysocki 2018-04-05 294 ktime_t delta_next;
4f86d3a8e Len Brown 2007-10-03 295
672917dcc Corrado Zoccolo 2009-09-21 296 if (data->needs_update) {
46bcfad7a Deepthi Dharwar 2011-10-28 297 menu_update(drv, dev);
672917dcc Corrado Zoccolo 2009-09-21 298 data->needs_update = 0;
672917dcc Corrado Zoccolo 2009-09-21 299 }
672917dcc Corrado Zoccolo 2009-09-21 300
69d25870f Arjan van de Ven 2009-09-21 301 /* Special case when user has set very strict latency requirement */
45f1ff59e Rafael J. Wysocki 2018-03-22 302 if (unlikely(latency_req == 0)) {
45f1ff59e Rafael J. Wysocki 2018-03-22 303 *stop_tick = false;
a2bd92023 venkatesh.pallipadi@...el.com 2008-07-30 304 return 0;
45f1ff59e Rafael J. Wysocki 2018-03-22 305 }
a2bd92023 venkatesh.pallipadi@...el.com 2008-07-30 306
69d25870f Arjan van de Ven 2009-09-21 307 /* determine the expected residency time, round up */
296bb1e51 Rafael J. Wysocki 2018-04-05 308 data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next));
69d25870f Arjan van de Ven 2009-09-21 309
5f9f09809 Rafael J. Wysocki 2018-08-10 310 /*
5f9f09809 Rafael J. Wysocki 2018-08-10 311 * If the tick is already stopped, the cost of possible short idle
5f9f09809 Rafael J. Wysocki 2018-08-10 312 * duration misprediction is much higher, because the CPU may be stuck
5f9f09809 Rafael J. Wysocki 2018-08-10 313 * in a shallow idle state for a long time as a result of it. In that
5f9f09809 Rafael J. Wysocki 2018-08-10 314 * case say we might mispredict and use the known time till the closest
5f9f09809 Rafael J. Wysocki 2018-08-10 315 * timer event for the idle state selection.
5f9f09809 Rafael J. Wysocki 2018-08-10 316 */
5f9f09809 Rafael J. Wysocki 2018-08-10 317 if (tick_nohz_tick_stopped()) {
5f9f09809 Rafael J. Wysocki 2018-08-10 318 data->predicted_us = ktime_to_us(delta_next);
5f9f09809 Rafael J. Wysocki 2018-08-10 319 goto select;
^^^^^^^^^^^
We hit this goto
5f9f09809 Rafael J. Wysocki 2018-08-10 320 }
5f9f09809 Rafael J. Wysocki 2018-08-10 321
372ba8cb4 Mel Gorman 2014-08-06 322 get_iowait_load(&nr_iowaiters, &cpu_load);
64b4ca5cb Mel Gorman 2014-08-06 323 data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
69d25870f Arjan van de Ven 2009-09-21 324
69d25870f Arjan van de Ven 2009-09-21 325 /*
51f245b89 Tuukka Tikkanen 2013-08-14 326 * Force the result of multiplication to be 64 bits even if both
51f245b89 Tuukka Tikkanen 2013-08-14 327 * operands are 32 bits.
51f245b89 Tuukka Tikkanen 2013-08-14 328 * Make sure to round up for half microseconds.
51f245b89 Tuukka Tikkanen 2013-08-14 329 */
ee3c86f35 Javi Merino 2015-04-16 330 data->predicted_us = DIV_ROUND_CLOSEST_ULL((uint64_t)data->next_timer_us *
51f245b89 Tuukka Tikkanen 2013-08-14 331 data->correction_factor[data->bucket],
69d25870f Arjan van de Ven 2009-09-21 332 RESOLUTION * DECAY);
69d25870f Arjan van de Ven 2009-09-21 333
e132b9b3b Rik van Riel 2016-03-16 334 expected_interval = get_typical_interval(data);
e132b9b3b Rik van Riel 2016-03-16 335 expected_interval = min(expected_interval, data->next_timer_us);
96e95182e tuukka.tikkanen@...aro.org 2014-02-24 336
dc2251bf9 Rafael J. Wysocki 2017-08-23 337 first_idx = 0;
dc2251bf9 Rafael J. Wysocki 2017-08-23 338 if (drv->states[0].flags & CPUIDLE_FLAG_POLLING) {
dc2251bf9 Rafael J. Wysocki 2017-08-23 339 struct cpuidle_state *s = &drv->states[1];
0c313cb20 Rafael J. Wysocki 2016-03-20 340 unsigned int polling_threshold;
0c313cb20 Rafael J. Wysocki 2016-03-20 341
96e95182e tuukka.tikkanen@...aro.org 2014-02-24 342 /*
69d25870f Arjan van de Ven 2009-09-21 343 * We want to default to C1 (hlt), not to busy polling
e132b9b3b Rik van Riel 2016-03-16 344 * unless the timer is happening really really soon, or
e132b9b3b Rik van Riel 2016-03-16 345 * C1's exit latency exceeds the user configured limit.
69d25870f Arjan van de Ven 2009-09-21 346 */
0c313cb20 Rafael J. Wysocki 2016-03-20 347 polling_threshold = max_t(unsigned int, 20, s->target_residency);
0c313cb20 Rafael J. Wysocki 2016-03-20 348 if (data->next_timer_us > polling_threshold &&
0c313cb20 Rafael J. Wysocki 2016-03-20 349 latency_req > s->exit_latency && !s->disabled &&
dc2251bf9 Rafael J. Wysocki 2017-08-23 350 !dev->states_usage[1].disable)
dc2251bf9 Rafael J. Wysocki 2017-08-23 351 first_idx = 1;
9c4b2867e Rafael J. Wysocki 2016-01-14 352 }
4f86d3a8e Len Brown 2007-10-03 353
71abbbf85 Ai Li 2010-08-09 354 /*
e132b9b3b Rik van Riel 2016-03-16 355 * Use the lowest expected idle interval to pick the idle state.
e132b9b3b Rik van Riel 2016-03-16 356 */
e132b9b3b Rik van Riel 2016-03-16 357 data->predicted_us = min(data->predicted_us, expected_interval);
e132b9b3b Rik van Riel 2016-03-16 358
e132b9b3b Rik van Riel 2016-03-16 359 /*
5f9f09809 Rafael J. Wysocki 2018-08-10 360 * Use the performance multiplier and the user-configurable latency_req
5f9f09809 Rafael J. Wysocki 2018-08-10 361 * to determine the maximum exit latency.
e132b9b3b Rik van Riel 2016-03-16 362 */
e132b9b3b Rik van Riel 2016-03-16 363 interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
e132b9b3b Rik van Riel 2016-03-16 364 if (latency_req > interactivity_req)
e132b9b3b Rik van Riel 2016-03-16 365 latency_req = interactivity_req;
e132b9b3b Rik van Riel 2016-03-16 366
5f9f09809 Rafael J. Wysocki 2018-08-10 367 select:
45f1ff59e Rafael J. Wysocki 2018-03-22 368 expected_interval = data->predicted_us;
e132b9b3b Rik van Riel 2016-03-16 369 /*
71abbbf85 Ai Li 2010-08-09 370 * Find the idle state with the lowest power while satisfying
71abbbf85 Ai Li 2010-08-09 371 * our constraints.
71abbbf85 Ai Li 2010-08-09 372 */
3ed09c945 Nicholas Piggin 2017-06-26 373 idx = -1;
3ed09c945 Nicholas Piggin 2017-06-26 @374 for (i = first_idx; i < drv->state_count; i++) {
^^^^^^^^^^^^^^
This is uninitialized
46bcfad7a Deepthi Dharwar 2011-10-28 375 struct cpuidle_state *s = &drv->states[i];
dc7fd275a ShuoX Liu 2012-07-03 376 struct cpuidle_state_usage *su = &dev->states_usage[i];
4f86d3a8e Len Brown 2007-10-03 377
cbc9ef028 Rafael J. Wysocki 2012-07-03 378 if (s->disabled || su->disable)
3a53396b0 ShuoX Liu 2012-03-28 379 continue;
3ed09c945 Nicholas Piggin 2017-06-26 380 if (idx == -1)
3ed09c945 Nicholas Piggin 2017-06-26 381 idx = i; /* first enabled state */
148519120 Rafael J. Wysocki 2013-07-27 382 if (s->target_residency > data->predicted_us)
8e37e1a2a Alex Shi 2017-01-12 383 break;
45f1ff59e Rafael J. Wysocki 2018-03-22 384 if (s->exit_latency > latency_req) {
45f1ff59e Rafael J. Wysocki 2018-03-22 385 /*
45f1ff59e Rafael J. Wysocki 2018-03-22 386 * If we break out of the loop for latency reasons, use
45f1ff59e Rafael J. Wysocki 2018-03-22 387 * the target residency of the selected state as the
45f1ff59e Rafael J. Wysocki 2018-03-22 388 * expected idle duration so that the tick is retained
45f1ff59e Rafael J. Wysocki 2018-03-22 389 * as long as that target residency is low enough.
45f1ff59e Rafael J. Wysocki 2018-03-22 390 */
45f1ff59e Rafael J. Wysocki 2018-03-22 391 expected_interval = drv->states[idx].target_residency;
8e37e1a2a Alex Shi 2017-01-12 392 break;
45f1ff59e Rafael J. Wysocki 2018-03-22 393 }
3ed09c945 Nicholas Piggin 2017-06-26 394 idx = i;
71abbbf85 Ai Li 2010-08-09 395 }
4f86d3a8e Len Brown 2007-10-03 396
3ed09c945 Nicholas Piggin 2017-06-26 397 if (idx == -1)
3ed09c945 Nicholas Piggin 2017-06-26 398 idx = 0; /* No states enabled. Must use 0. */
3ed09c945 Nicholas Piggin 2017-06-26 399
45f1ff59e Rafael J. Wysocki 2018-03-22 400 /*
45f1ff59e Rafael J. Wysocki 2018-03-22 401 * Don't stop the tick if the selected state is a polling one or if the
45f1ff59e Rafael J. Wysocki 2018-03-22 402 * expected idle duration is shorter than the tick period length.
45f1ff59e Rafael J. Wysocki 2018-03-22 403 */
5f9f09809 Rafael J. Wysocki 2018-08-10 404 if (((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
5f9f09809 Rafael J. Wysocki 2018-08-10 405 expected_interval < TICK_USEC) && !tick_nohz_tick_stopped()) {
296bb1e51 Rafael J. Wysocki 2018-04-05 406 unsigned int delta_next_us = ktime_to_us(delta_next);
296bb1e51 Rafael J. Wysocki 2018-04-05 407
45f1ff59e Rafael J. Wysocki 2018-03-22 408 *stop_tick = false;
45f1ff59e Rafael J. Wysocki 2018-03-22 409
5f9f09809 Rafael J. Wysocki 2018-08-10 410 if (idx > 0 && drv->states[idx].target_residency > delta_next_us) {
296bb1e51 Rafael J. Wysocki 2018-04-05 411 /*
296bb1e51 Rafael J. Wysocki 2018-04-05 412 * The tick is not going to be stopped and the target
296bb1e51 Rafael J. Wysocki 2018-04-05 413 * residency of the state to be returned is not within
296bb1e51 Rafael J. Wysocki 2018-04-05 414 * the time until the next timer event including the
296bb1e51 Rafael J. Wysocki 2018-04-05 415 * tick, so try to correct that.
296bb1e51 Rafael J. Wysocki 2018-04-05 416 */
296bb1e51 Rafael J. Wysocki 2018-04-05 417 for (i = idx - 1; i >= 0; i--) {
296bb1e51 Rafael J. Wysocki 2018-04-05 418 if (drv->states[i].disabled ||
296bb1e51 Rafael J. Wysocki 2018-04-05 419 dev->states_usage[i].disable)
296bb1e51 Rafael J. Wysocki 2018-04-05 420 continue;
296bb1e51 Rafael J. Wysocki 2018-04-05 421
296bb1e51 Rafael J. Wysocki 2018-04-05 422 idx = i;
296bb1e51 Rafael J. Wysocki 2018-04-05 423 if (drv->states[i].target_residency <= delta_next_us)
296bb1e51 Rafael J. Wysocki 2018-04-05 424 break;
296bb1e51 Rafael J. Wysocki 2018-04-05 425 }
296bb1e51 Rafael J. Wysocki 2018-04-05 426 }
296bb1e51 Rafael J. Wysocki 2018-04-05 427 }
296bb1e51 Rafael J. Wysocki 2018-04-05 428
3ed09c945 Nicholas Piggin 2017-06-26 429 data->last_state_idx = idx;
3ed09c945 Nicholas Piggin 2017-06-26 430
69d25870f Arjan van de Ven 2009-09-21 431 return data->last_state_idx;
4f86d3a8e Len Brown 2007-10-03 432 }
4f86d3a8e Len Brown 2007-10-03 433
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