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([110.9.142.4]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-87feac93380sm2823606b3a.33.2026.09.27.02.18.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Sep 2026 02:18:10 -0700 (PDT) From: Sang-Heon Jeon To: Petr Mladek Cc: John Ogness , linux-kernel@vger.kernel.org, Sergey Senozhatsky , Steven Rostedt Subject: [PATCH v2] printk: increase the ring buffer for more than 16 CPUs by default Date: Sun, 27 Sep 2026 18:17:54 +0900 Message-ID: <20260927091756.50831-1-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 more than 17 CPUs. Remove the explicit subtraction of one, so the ring buffer is increased for more than 16 CPUs, which is a power of two. Also fix the outdated comment. Suggested-by: Petr Mladek Signed-off-by: Sang-Heon Jeon --- Changes from v1 [1] - Adjust default threshold to power of two, as suggested by Petr [1] https://lore.kernel.org/all/20260921163828.111061-1-ekffu200098@gmail.com/ --- kernel/printk/printk.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 00f8e1291564..1ba440c1193e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1085,9 +1085,9 @@ static void __init log_buf_add_cpu(void) if (num_possible_cpus() == 1) return; - cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN; + cpu_extra = num_possible_cpus() * __LOG_CPU_MAX_BUF_LEN; - /* by default this will only continue through for large > 64 CPUs */ + /* by default this will only continue through for more than 16 CPUs */ if (cpu_extra <= __LOG_BUF_LEN / 2) return; base-commit: b03d22ec8186f3f6b40b95a5a678100cf80116cb -- 2.43.0