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printk: increase the ring buffer for more than 16 CPUs by default

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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 Also fix the outdated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 <pmladek@suse.com>
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20260927091756.50831-1-ekffu200098@gmail.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Sang-Heon Jeon 2026-09-27 18:17:54 +09:00 committed by Petr Mladek
parent 267f1127c0
commit ae30792e53
1 changed files with 2 additions and 2 deletions
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4
kernel/printk/printk.c
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@ -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;