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When tasks come and go from a runqueue quickly, this can lead to boost being applied and removed quickly which sometimes means we cannot raise the CPU frequency again when we need to (due to the rate limit on frequency updates). This has proved to be a particular issue for RT tasks and alternative methods have been used in the past to work around it. This is an attempt to solve the issue for all task classes and cpufreq governors by introducing a generic mechanism in schedtune to retain the max boost level from task enqueue for a minimum period - defined here as 50ms. This timeout was determined experimentally and is not configurable. A sched_feat guards the application of this to tasks - in the default configuration, task boosting only applied to tasks which have RT policy. Change SCHEDTUNE_BOOST_HOLD_ALL to true to apply it to all tasks regardless of class. It works like so: Every task enqueue (in an allowed class) stores a cpu-local timestamp. If the task is not a member of an allowed class (all or RT depending upon feature selection), the timestamp is not updated. The boost group will stay active regardless of tasks present until 50ms beyond the last timestamp stored. We also store the timestamp of the active boost group to avoid unneccesarily revisiting the boost groups when checking CPU boost level. If the timestamp is more than 50ms in the past when we check boost then we re-evaluate the boost groups for that CPU, taking into account the timestamps associated with each group. Idea based on rt-boost-retention patches from Joel. Change-Id: I52cc2d2e82d1c5aa03550378c8836764f41630c1 Suggested-by: Joel Fernandes <joelaf@google.com> Reviewed-by: Patrick Bellasi <patrick.bellasi@arm.com> Signed-off-by: Chris Redpath <chris.redpath@arm.com> [forward ported from android-4.9-eas-dev proposal] (cherry picked from commit a485e8b7bf8e95759e600396feeb7bfb400b6e46) [ - Trivial cherry-pick conflicts in include/trace/events/sched.h ] Signed-off-by: Quentin Perret <quentin.perret@arm.com>
123 lines
3.3 KiB
C
123 lines
3.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Only give sleepers 50% of their service deficit. This allows
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* them to run sooner, but does not allow tons of sleepers to
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* rip the spread apart.
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*/
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SCHED_FEAT(GENTLE_FAIR_SLEEPERS, true)
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/*
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* Place new tasks ahead so that they do not starve already running
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* tasks
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*/
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SCHED_FEAT(START_DEBIT, true)
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/*
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* Prefer to schedule the task we woke last (assuming it failed
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* wakeup-preemption), since its likely going to consume data we
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* touched, increases cache locality.
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*/
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SCHED_FEAT(NEXT_BUDDY, false)
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/*
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* Prefer to schedule the task that ran last (when we did
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* wake-preempt) as that likely will touch the same data, increases
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* cache locality.
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*/
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SCHED_FEAT(LAST_BUDDY, true)
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/*
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* Consider buddies to be cache hot, decreases the likelyness of a
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* cache buddy being migrated away, increases cache locality.
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*/
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SCHED_FEAT(CACHE_HOT_BUDDY, true)
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/*
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* Allow wakeup-time preemption of the current task:
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*/
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SCHED_FEAT(WAKEUP_PREEMPTION, true)
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SCHED_FEAT(HRTICK, false)
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SCHED_FEAT(DOUBLE_TICK, false)
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SCHED_FEAT(LB_BIAS, true)
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/*
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* Decrement CPU capacity based on time not spent running tasks
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*/
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SCHED_FEAT(NONTASK_CAPACITY, true)
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/*
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* Queue remote wakeups on the target CPU and process them
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* using the scheduler IPI. Reduces rq->lock contention/bounces.
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*/
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SCHED_FEAT(TTWU_QUEUE, true)
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/*
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* When doing wakeups, attempt to limit superfluous scans of the LLC domain.
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*/
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SCHED_FEAT(SIS_AVG_CPU, false)
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SCHED_FEAT(SIS_PROP, true)
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/*
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* Issue a WARN when we do multiple update_rq_clock() calls
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* in a single rq->lock section. Default disabled because the
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* annotations are not complete.
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*/
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SCHED_FEAT(WARN_DOUBLE_CLOCK, false)
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#ifdef HAVE_RT_PUSH_IPI
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/*
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* In order to avoid a thundering herd attack of CPUs that are
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* lowering their priorities at the same time, and there being
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* a single CPU that has an RT task that can migrate and is waiting
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* to run, where the other CPUs will try to take that CPUs
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* rq lock and possibly create a large contention, sending an
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* IPI to that CPU and let that CPU push the RT task to where
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* it should go may be a better scenario.
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*/
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SCHED_FEAT(RT_PUSH_IPI, true)
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#endif
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SCHED_FEAT(RT_RUNTIME_SHARE, true)
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SCHED_FEAT(LB_MIN, false)
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SCHED_FEAT(ATTACH_AGE_LOAD, true)
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SCHED_FEAT(WA_IDLE, true)
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SCHED_FEAT(WA_WEIGHT, true)
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SCHED_FEAT(WA_BIAS, true)
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/*
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* UtilEstimation. Use estimated CPU utilization.
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*/
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SCHED_FEAT(UTIL_EST, true)
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/*
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* Fast pre-selection of CPU candidates for EAS.
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*/
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SCHED_FEAT(FIND_BEST_TARGET, true)
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/*
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* Energy aware scheduling algorithm choices:
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* EAS_PREFER_IDLE
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* Direct tasks in a schedtune.prefer_idle=1 group through
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* the EAS path for wakeup task placement. Otherwise, put
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* those tasks through the mainline slow path.
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*/
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SCHED_FEAT(EAS_PREFER_IDLE, true)
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/*
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* Request max frequency from schedutil whenever a RT task is running.
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*/
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SCHED_FEAT(SUGOV_RT_MAX_FREQ, false)
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/*
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* Apply schedtune boost hold to tasks of all sched classes.
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* If enabled, schedtune will hold the boost applied to a CPU
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* for 50ms regardless of task activation - if the task is
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* still running 50ms later, the boost hold expires and schedtune
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* boost will expire immediately the task stops.
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* If disabled, this behaviour will only apply to tasks of the
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* RT class.
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*/
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SCHED_FEAT(SCHEDTUNE_BOOST_HOLD_ALL, false)
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