Commit fa167475 authored Jun 21, 2019 by Patrick Bellasi Committed by Quentin Perret Feb 01, 2020

UPSTREAM: sched/uclamp: Set default clamps for RT tasks



By default FAIR tasks start without clamps, i.e. neither boosted nor
capped, and they run at the best frequency matching their utilization
demand.  This default behavior does not fit RT tasks which instead are
expected to run at the maximum available frequency, if not otherwise
required by explicitly capping them.

Enforce the correct behavior for RT tasks by setting util_min to max
whenever:

 1. the task is switched to the RT class and it does not already have a
    user-defined clamp value assigned.

 2. an RT task is forked from a parent with RESET_ON_FORK set.

NOTE: utilization clamp values are cross scheduling class attributes and
thus they are never changed/reset once a value has been explicitly
defined from user-space.

Bug: 120440300
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alessio Balsini <balsini@android.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@google.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lkml.kernel.org/r/20190621084217.8167-9-patrick.bellasi@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1a00d999971c78ab024a17b0efc37d78404dd120)
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Change-Id: I81fcadaea34f557e531fa5ac6aab84fcb0ee37c7
Signed-off-by: Quentin Perret <qperret@google.com>

parent 341f6109

kernel/sched/core.c

+28 −2

Original line number	Diff line number	Diff line
		@@ -1017,6 +1017,27 @@ static int uclamp_validate(struct task_struct *p,
		static void __setscheduler_uclamp(struct task_struct *p,
		const struct sched_attr *attr)
		{
		unsigned int clamp_id;

		/*
		* On scheduling class change, reset to default clamps for tasks
		* without a task-specific value.
		*/
		for_each_clamp_id(clamp_id) {
		struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
		unsigned int clamp_value = uclamp_none(clamp_id);

		/* Keep using defined clamps across class changes */
		if (uc_se->user_defined)
		continue;

		/* By default, RT tasks always get 100% boost */
		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
		clamp_value = uclamp_none(UCLAMP_MAX);

		uclamp_se_set(uc_se, clamp_value, false);
		}

		if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
		return;

		@@ -1042,8 +1063,13 @@ static void uclamp_fork(struct task_struct *p)
		return;

		for_each_clamp_id(clamp_id) {
		uclamp_se_set(&p->uclamp_req[clamp_id],
		uclamp_none(clamp_id), false);
		unsigned int clamp_value = uclamp_none(clamp_id);

		/* By default, RT tasks always get 100% boost */
		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
		clamp_value = uclamp_none(UCLAMP_MAX);

		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
		}
		}