linux-kernel - [PATCH 5/7 v2] sched/balancing: Update run_rebalance

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Message-ID: <ZeG7dt50PCQ8fFHw@gmail.com>
Date: Fri, 1 Mar 2024 12:26:46 +0100
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Valentin Schneider <vschneid@...hat.com>
Subject: [PATCH 5/7 v2] sched/balancing: Update run_rebalance_domains()
 comments


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@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Valentin Schneider <vschneid@...hat.com>
---
 kernel/sched/fair.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4c46bffb6a7a..18b7d2999cff 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12409,8 +12409,13 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 }
 
 /*
- * run_rebalance_domains is triggered when needed from the scheduler tick.
- * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).
+ * The run_rebalance_domains() softirq handler is triggered via SCHED_SOFTIRQ
+ * from two places:
+ *
+ *  - the scheduler_tick(),
+ *
+ *  - from the SMP cross-call function nohz_csd_func(),
+ *    used by NOHZ idle balancing (with NOHZ_BALANCE_KICK set).
  */
 static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
 {