linux-kernel - [tip: sched/core] sched/balancing: Update run_rebalance

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Date: Tue, 12 Mar 2024 12:00:30 -0000
From: "tip-bot2 for Ingo Molnar" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Ingo Molnar <mingo@...nel.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: sched/core] sched/balancing: Update run_rebalance_domains() comments

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

Commit-ID:     3dc6f6c8efe2d9148865664fffbe9dd89fb0d157
Gitweb:        https://git.kernel.org/tip/3dc6f6c8efe2d9148865664fffbe9dd89fb0d157
Author:        Ingo Molnar <mingo@...nel.org>
AuthorDate:    Fri, 08 Mar 2024 11:58:59 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 12 Mar 2024 11:59:43 +01:00

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>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Acked-by: Valentin Schneider <vschneid@...hat.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-9-mingo@kernel.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 f3c03c6..b567c07 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12409,9 +12409,12 @@ out:
 }
 
 /*
- * 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)
 {