diff options
| -rw-r--r-- | Documentation/kernel-parameters.txt | 5 | ||||
| -rw-r--r-- | include/linux/jiffies.h | 2 | ||||
| -rw-r--r-- | init/calibrate.c | 2 | ||||
| -rw-r--r-- | kernel/printk.c | 59 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 18 |
5 files changed, 85 insertions, 1 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 085e4a095eaa..760ed5776174 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -349,6 +349,11 @@ and is between 256 and 4096 characters. It is defined in the file blkmtd_bs= blkmtd_count= + boot_delay= Milliseconds to delay each printk during boot. + Values larger than 10 seconds (10000) are changed to + no delay (0). + Format: integer + bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) bttv.radio= Most important insmod options are available as kernel args too. diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index e757a74b9d17..8b080024bbc1 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -148,6 +148,8 @@ static inline u64 get_jiffies_64(void) */ #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1) +extern unsigned long preset_lpj; + /* * We want to do realistic conversions of time so we need to use the same * values the update wall clock code uses as the jiffies size. This value diff --git a/init/calibrate.c b/init/calibrate.c index 40ff3b404895..2d3d73bd4ce1 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -10,7 +10,7 @@ #include <asm/timex.h> -static unsigned long preset_lpj; +unsigned long preset_lpj; static int __init lpj_setup(char *str) { preset_lpj = simple_strtoul(str,NULL,0); diff --git a/kernel/printk.c b/kernel/printk.c index 8451dfc31d25..b2b5c3a22a36 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -22,6 +22,8 @@ #include <linux/tty_driver.h> #include <linux/console.h> #include <linux/init.h> +#include <linux/jiffies.h> +#include <linux/nmi.h> #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/interrupt.h> /* For in_interrupt() */ @@ -162,6 +164,61 @@ out: __setup("log_buf_len=", log_buf_len_setup); +#ifdef CONFIG_BOOT_PRINTK_DELAY + +static unsigned int boot_delay; /* msecs delay after each printk during bootup */ +static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */ + +static int __init boot_delay_setup(char *str) +{ + unsigned long lpj; + unsigned long long loops_per_msec; + + lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */ + loops_per_msec = (unsigned long long)lpj / 1000 * HZ; + + get_option(&str, &boot_delay); + if (boot_delay > 10 * 1000) + boot_delay = 0; + + printk_delay_msec = loops_per_msec; + printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, " + "HZ: %d, printk_delay_msec: %llu\n", + boot_delay, preset_lpj, lpj, HZ, printk_delay_msec); + return 1; +} +__setup("boot_delay=", boot_delay_setup); + +static void boot_delay_msec(void) +{ + unsigned long long k; + unsigned long timeout; + + if (boot_delay == 0 || system_state != SYSTEM_BOOTING) + return; + + k = (unsigned long long)printk_delay_msec * boot_delay; + + timeout = jiffies + msecs_to_jiffies(boot_delay); + while (k) { + k--; + cpu_relax(); + /* + * use (volatile) jiffies to prevent + * compiler reduction; loop termination via jiffies + * is secondary and may or may not happen. + */ + if (time_after(jiffies, timeout)) + break; + touch_nmi_watchdog(); + } +} +#else +static inline void boot_delay_msec(void) +{ +} +#endif + /* * Commands to do_syslog: * @@ -527,6 +584,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) static char printk_buf[1024]; static int log_level_unknown = 1; + boot_delay_msec(); + preempt_disable(); if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id()) /* If a crash is occurring during printk() on this CPU, diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 396c38b3cb69..7d16e6433302 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -413,6 +413,24 @@ config FORCED_INLINING become the default in the future, until then this option is there to test gcc for this. +config BOOT_PRINTK_DELAY + bool "Delay each boot printk message by N milliseconds" + depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY + help + This build option allows you to read kernel boot messages + by inserting a short delay after each one. The delay is + specified in milliseconds on the kernel command line, + using "boot_delay=N". + + It is likely that you would also need to use "lpj=M" to preset + the "loops per jiffie" value. + See a previous boot log for the "lpj" value to use for your + system, and then set "lpj=M" before setting "boot_delay=N". + NOTE: Using this option may adversely affect SMP systems. + I.e., processors other than the first one may not boot up. + BOOT_PRINTK_DELAY also may cause DETECT_SOFTLOCKUP to detect + what it believes to be lockup conditions. + config RCU_TORTURE_TEST tristate "torture tests for RCU" depends on DEBUG_KERNEL |