Commit d81ae8aa authored Jun 30, 2020 by Qais Yousef Committed by Peter Zijlstra Jul 08, 2020

sched/uclamp: Fix initialization of struct uclamp_rq



struct uclamp_rq was zeroed out entirely in assumption that in the first
call to uclamp_rq_inc() they'd be initialized correctly in accordance to
default settings.

But when next patch introduces a static key to skip
uclamp_rq_{inc,dec}() until userspace opts in to use uclamp, schedutil
will fail to perform any frequency changes because the
rq->uclamp[UCLAMP_MAX].value is zeroed at init and stays as such. Which
means all rqs are capped to 0 by default.

Fix it by making sure we do proper initialization at init without
relying on uclamp_rq_inc() doing it later.

Fixes: 69842cba ("sched/uclamp: Add CPU's clamp buckets refcounting")
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lkml.kernel.org/r/20200630112123.12076-2-qais.yousef@arm.com

parent 85c2ce91

kernel/sched/core.c

+16 −5

Original line number	Diff line number	Diff line
		@@ -1239,6 +1239,20 @@ static void uclamp_fork(struct task_struct *p)
		}
		}

		static void __init init_uclamp_rq(struct rq *rq)
		{
		enum uclamp_id clamp_id;
		struct uclamp_rq *uc_rq = rq->uclamp;

		for_each_clamp_id(clamp_id) {
		uc_rq[clamp_id] = (struct uclamp_rq) {
		.value = uclamp_none(clamp_id)
		};
		}

		rq->uclamp_flags = 0;
		}

		static void __init init_uclamp(void)
		{
		struct uclamp_se uc_max = {};
		@@ -1247,11 +1261,8 @@ static void __init init_uclamp(void)

		mutex_init(&uclamp_mutex);

		for_each_possible_cpu(cpu) {
		memset(&cpu_rq(cpu)->uclamp, 0,
		sizeof(struct uclamp_rq)*UCLAMP_CNT);
		cpu_rq(cpu)->uclamp_flags = 0;
		}
		for_each_possible_cpu(cpu)
		init_uclamp_rq(cpu_rq(cpu));

		for_each_clamp_id(clamp_id) {
		uclamp_se_set(&init_task.uclamp_req[clamp_id],

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