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From:   Abel Wu <wuyun.abel@bytedance.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Josh Don <joshdon@google.com>, Chen Yu <yu.c.chen@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        "Gautham R . Shenoy" <gautham.shenoy@amd.com>,
        linux-kernel@vger.kernel.org, Abel Wu <wuyun.abel@bytedance.com>
Subject: [PATCH v5 3/5] sched/fair: Skip core update if task pending
Date:   Fri,  9 Sep 2022 13:53:02 +0800
Message-Id: <20220909055304.25171-4-wuyun.abel@bytedance.com>
In-Reply-To: <20220909055304.25171-1-wuyun.abel@bytedance.com>
References: <20220909055304.25171-1-wuyun.abel@bytedance.com>
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The function __update_idle_core() considers this cpu is idle so
only checks its siblings to decide whether the resident core is
idle or not and update has_idle_cores hint if necessary. But the
problem is that this cpu might not be idle at that moment any
more, resulting in the hint being misleading.

It's not proper to make this check everywhere in the idle path,
but checking just before core updating can make the has_idle_core
hint more reliable with negligible cost.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
---
 kernel/sched/fair.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7abe188a1533..fad289530e07 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6294,6 +6294,9 @@ void __update_idle_core(struct rq *rq)
 	int core = cpu_of(rq);
 	int cpu;
 
+	if (rq->ttwu_pending)
+		return;
+
 	rcu_read_lock();
 	if (test_idle_cores(core, true))
 		goto unlock;
-- 
2.37.3