Received-SPF: pass (google.com: domain of linux-kernel+bounces-96889-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Shrikanth Hegde <sshegde@linux.ibm.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH 08/10] sched/balancing: Update run_rebalance_domains() comments
Date: Fri,  8 Mar 2024 11:58:59 +0100
Message-Id: <20240308105901.1096078-9-mingo@kernel.org>
In-Reply-To: <20240308105901.1096078-1-mingo@kernel.org>
References: <20240308105901.1096078-1-mingo@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

The first sentence of the comment explaining run_rebalance_domains()
is historic and not true anymore:

    * run_rebalance_domains is triggered when needed from the scheduler tick.

.. contradicted/modified by the second sentence:

    * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).

Avoid that kind of confusion straight away and explain from what
places sched_balance_softirq() is triggered.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f3c03c6db3c8..b567c0790f44 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12409,9 +12409,12 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 }
 
 /*
- * This softirq may be triggered from the scheduler tick, or by
- * any of the flags in NOHZ_KICK_MASK: NOHZ_BALANCE_KICK,
- * NOHZ_STATS_KICK or NOHZ_NEXT_KICK.
+ * This softirq handler is triggered via SCHED_SOFTIRQ from two places:
+ *
+ * - directly from the local scheduler_tick() for periodic load balancing
+ *
+ * - indirectly from a remote scheduler_tick() for NOHZ idle balancing
+ *   through the SMP cross-call nohz_csd_func()
  */
 static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
 {
-- 
2.40.1