linux-kernel - [tip: sched/core] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu

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Date:   Mon, 19 Jun 2023 11:04:50 -0000
From:   "tip-bot2 for Hao Jia" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Hao Jia <jiahao.os@...edance.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/core: Avoid double calling update_rq_clock()
 in __balance_push_cpu_stop()

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     96500560f0c73c71bca1b27536c6254fa0e8ce37
Gitweb:        https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
Author:        Hao Jia <jiahao.os@...edance.com>
AuthorDate:    Tue, 13 Jun 2023 16:20:10 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00

sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

There is a double update_rq_clock() invocation:

  __balance_push_cpu_stop()
    update_rq_clock()
    __migrate_task()
      update_rq_clock()

Sadly select_fallback_rq() also needs update_rq_clock() for
__do_set_cpus_allowed(), it is not possible to remove the update from
__balance_push_cpu_stop(). So remove it from __migrate_task() and
ensure all callers of this function call update_rq_clock() prior to
calling it.

Signed-off-by: Hao Jia <jiahao.os@...edance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lkml.kernel.org/r/20230613082012.49615-3-jiahao.os@bytedance.com
---
 kernel/sched/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 442efe5..c7db597 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2546,7 +2546,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
 	if (!is_cpu_allowed(p, dest_cpu))
 		return rq;
 
-	update_rq_clock(rq);
 	rq = move_queued_task(rq, rf, p, dest_cpu);
 
 	return rq;
@@ -2604,10 +2603,12 @@ static int migration_cpu_stop(void *data)
 				goto out;
 		}
 
-		if (task_on_rq_queued(p))
+		if (task_on_rq_queued(p)) {
+			update_rq_clock(rq);
 			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
-		else
+		} else {
 			p->wake_cpu = arg->dest_cpu;
+		}
 
 		/*
 		 * XXX __migrate_task() can fail, at which point we might end