diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 883901b9ac4f11d0ea47d42769c8ee3c6e3e3360..9344d833b7ea231d42ecf7731851f71f9602033e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1716,8 +1716,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
7 (KERN_DEBUG) debug-level messages
log_buf_len=n[KMG] Sets the size of the printk ring buffer,
- in bytes. n must be a power of two. The default
- size is set in the kernel config file.
+ in bytes. n must be a power of two and greater
+ than the minimal size. The minimal size is defined
+ by LOG_BUF_SHIFT kernel config parameter. There is
+ also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
+ that allows to increase the default size depending on
+ the number of CPUs. See init/Kconfig for more details.
logo.nologo [FB] Disables display of the built-in Linux logo.
This may be used to provide more screen space for
diff --git a/init/Kconfig b/init/Kconfig
index 41066e49e8809464651d8335de4a77165a864033..a291b7ef473893891481f188b81f7dfce1550942 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -807,15 +807,53 @@ config LOG_BUF_SHIFT
range 12 21
default 17
help
- Select kernel log buffer size as a power of 2.
+ Select the minimal kernel log buffer size as a power of 2.
+ The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
+ parameter, see below. Any higher size also might be forced
+ by "log_buf_len" boot parameter.
+
Examples:
- 17 => 128 KB
+ 17 => 128 KB
16 => 64 KB
- 15 => 32 KB
- 14 => 16 KB
+ 15 => 32 KB
+ 14 => 16 KB
13 => 8 KB
12 => 4 KB
+config LOG_CPU_MAX_BUF_SHIFT
+ int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
+ range 0 21
+ default 12 if !BASE_SMALL
+ default 0 if BASE_SMALL
+ help
+ This option allows to increase the default ring buffer size
+ according to the number of CPUs. The value defines the contribution
+ of each CPU as a power of 2. The used space is typically only few
+ lines however it might be much more when problems are reported,
+ e.g. backtraces.
+
+ The increased size means that a new buffer has to be allocated and
+ the original static one is unused. It makes sense only on systems
+ 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 64 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.
+
+ The number of possible CPUs is used for this computation ignoring
+ hotplugging making the compuation optimal for the the worst case
+ scenerio while allowing a simple algorithm to be used from bootup.
+
+ Examples shift values and their meaning:
+ 17 => 128 KB for each CPU
+ 16 => 64 KB for each CPU
+ 15 => 32 KB for each CPU
+ 14 => 16 KB for each CPU
+ 13 => 8 KB for each CPU
+ 12 => 4 KB for each CPU
+
#
# Architectures with an unreliable sched_clock() should select this:
#
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index db290be32984db20119265aecf41a2cbc2ca7ffa..f855ec36dff9a4a887b41212363e04db67a56802 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -266,6 +266,7 @@ static u32 clear_idx;
#define LOG_ALIGN __alignof__(struct printk_log)
#endif
#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
+#define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;
@@ -848,12 +849,45 @@ static int __init log_buf_len_setup(char *str)
}
early_param("log_buf_len", log_buf_len_setup);
+static void __init log_buf_add_cpu(void)
+{
+ unsigned int cpu_extra;
+
+ /*
+ * archs should set up cpu_possible_bits properly with
+ * set_cpu_possible() after setup_arch() but just in
+ * case lets ensure this is valid.
+ */
+ if (num_possible_cpus() == 1)
+ return;
+
+ cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
+
+ /* by default this will only continue through for large > 64 CPUs */
+ if (cpu_extra <= __LOG_BUF_LEN / 2)
+ return;
+
+ pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
+ __LOG_CPU_MAX_BUF_LEN);
+ pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
+ cpu_extra);
+ pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
+
+ log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
+}
+
void __init setup_log_buf(int early)
{
unsigned long flags;
char *new_log_buf;
int free;
+ if (log_buf != __log_buf)
+ return;
+
+ if (!early && !new_log_buf_len)
+ log_buf_add_cpu();
+
if (!new_log_buf_len)
return;