Commit 1a00d999 authored Jun 21, 2019 by Patrick Bellasi Committed by Ingo Molnar Jun 24, 2019

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.

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>

parent a87498ac

kernel/sched/core.c

+28 −2

Original line number	Diff line number	Diff line
		@@ -1062,6 +1062,27 @@ 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;

		@@ -1087,8 +1108,13 @@ 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);
		}
		}

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