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Subject[tip: sched/core] sched/uclamp: Fix initialization of struct uclamp_rq
The following commit has been merged into the sched/core branch of tip:

Commit-ID: d81ae8aac85ca2e307d273f6dc7863a721bf054e
Gitweb: https://git.kernel.org/tip/d81ae8aac85ca2e307d273f6dc7863a721bf054e
Author: Qais Yousef <qais.yousef@arm.com>
AuthorDate: Tue, 30 Jun 2020 12:21:22 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 08 Jul 2020 11:39:01 +02:00

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: 69842cba9ace ("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
---
kernel/sched/core.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 15c980a..9605db7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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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