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SubjectRe: [PATCH 1/2] sched/uclamp: Fix initialization of strut uclamp_rq
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On 18/06/20 20:55, Qais Yousef wrote:
> 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>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> CC: Patrick Bellasi <patrick.bellasi@matbug.net>
> Cc: Chris Redpath <chrid.redpath@arm.com>
> Cc: Lukasz Luba <lukasz.luba@arm.com>
> Cc: linux-kernel@vger.kernel.org

Small nit below, otherwise:
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

> ---
> kernel/sched/core.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a43c84c27c6f..e19d2b915406 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1248,6 +1248,20 @@ 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) {
> + memset(uc_rq[clamp_id].bucket,
> + 0,
> + sizeof(struct uclamp_bucket)*UCLAMP_BUCKETS);
> +
> + uc_rq[clamp_id].value = uclamp_none(clamp_id);
> + }
> +}
> +
> static void __init init_uclamp(void)
> {
> struct uclamp_se uc_max = {};
> @@ -1257,8 +1271,7 @@ 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);
> + init_uclamp_rq(cpu_rq(cpu));
> cpu_rq(cpu)->uclamp_flags = 0;

That flags assignment ought to be squashed in the init function as well -
and actually you do that in patch 2, so I suppose that's a rebase accident.

> }

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