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([110.9.142.4]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc72ae8ff2bsm3812261a12.13.2026.09.21.09.38.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 09:38:57 -0700 (PDT) From: Sang-Heon Jeon To: Petr Mladek Cc: John Ogness , linux-kernel@vger.kernel.org, Sergey Senozhatsky , Steven Rostedt Subject: [PATCH] printk: fix wrong number of CPUs required to increase the ring buffer Date: Tue, 22 Sep 2026 01:38:27 +0900 Message-ID: <20260921163828.111061-1-ekffu200098@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The default LOG_BUF_SHIFT is 17, which means 128 KB, and LOG_CPU_MAX_BUF_SHIFT is 12, which means 4 KB per CPU. By default the ring buffer is increased when (num_possible_cpus() - 1) * 4 KB > 64 KB, which requires 18 or more CPUs. Fix the wrong comment and help text. Signed-off-by: Sang-Heon Jeon --- init/Kconfig | 2 +- kernel/printk/printk.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 60448fd4ee12..446cbb59a43b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -843,7 +843,7 @@ config LOG_CPU_MAX_BUF_SHIFT with more CPUs. Therefore this value is used only when the sum of contributions is greater than the half of the default kernel ring buffer as defined by LOG_BUF_SHIFT. The default values are set - so that more than 16 CPUs are needed to trigger the allocation. + so that 18 or more CPUs are needed to trigger the allocation. Also this option is ignored when "log_buf_len" kernel parameter is used as it forces an exact (power of two) size of the ring buffer. diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 00f8e1291564..c7d961256c88 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1087,7 +1087,7 @@ static void __init log_buf_add_cpu(void) cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN; - /* by default this will only continue through for large > 64 CPUs */ + /* by default this will only continue through for 18 or more CPUs */ if (cpu_extra <= __LOG_BUF_LEN / 2) return; base-commit: b03d22ec8186f3f6b40b95a5a678100cf80116cb -- 2.43.0