linux-kernel - [PATCH v2 0/1] timers/migration: add 'tmigr' kernel parameter to optionally disable timer migration

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Message-Id: <20250910074251.8148-1-sehee1.jeong@samsung.com>
Date: Wed, 10 Sep 2025 16:42:50 +0900
From: Sehee Jeong <sehee1.jeong@...sung.com>
To: anna-maria@...utronix.de, frederic@...nel.org, tglx@...utronix.de,
	corbet@....net
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	sehee1.jeong@...sung.com
Subject: [PATCH v2 0/1] timers/migration: add 'tmigr' kernel parameter to
 optionally disable timer migration

This patch introduces a kernel boot parameter to optionally disable the
timer migration.

On heterogeneous systems with big.LITTLE architectures, timer migration
may cause timers from little cores to run on big cores, or vice versa,
because core type differences are not considered in the current timer
migration logic.

In our heterogeneous system, we observed timers being migrated to big
CPU frequently, resulting in timer callbacks that could have run on
little CPUs being executed on the big CPU instead. This reduced big
CPU's idle residency and increased overall power consumption due to
higher power draw on the big CPU. Since timer_migration is a relatively
new feature, addressing the structural limitation was difficult.
Therefore, this patch adds a boot parameter to optionally disable timer
migration.

---
Changes in v2:
  - Added more description of potential issue in the commit message
  - Changed the boot parameter format to tmigr=[on|off]

Link: https://lore.kernel.org/r/20250807064849.3988-1-sehee1.jeong@samsung.com

Sehee Jeong (1):
  timers/migration: add 'tmigr' kernel parameter to optionally disable
    timer migration

 .../admin-guide/kernel-parameters.txt         |  4 ++++
 kernel/time/timer_migration.c                 | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

-- 
2.49.0