This one delays each printk() during boot by a variable time (from kernel command line), while system_state == SYSTEM_BOOTING. Caveat: it's not terribly SMP safe or SMP nice. Any ideas for improvements (esp. in the SMP area) are appreciated. --- From: Randy Dunlap <rdunlap@xenotime.net> Optionally add a boot delay after each kernel printk() call, crudely measured in milliseconds, with a maximum delay of 10 seconds per printk. Enable CONFIG_BOOT_DELAY=y and then add (e.g.): "lpj=loops_per_jiffy boot_delay=100" to the kernel command line. Signed-off-by: Randy Dunlap <rdunlap@xenotime.net> --- init/calibrate.c | 2 +- init/main.c | 25 +++++++++++++++++++++++++ kernel/printk.c | 33 +++++++++++++++++++++++++++++++++ lib/Kconfig.debug | 18 ++++++++++++++++++ 4 files changed, 77 insertions(+), 1 deletion(-) --- linux-2615-work.orig/init/main.c +++ linux-2615-work/init/main.c @@ -557,6 +557,31 @@ static int __init initcall_debug_setup(c } __setup("initcall_debug", initcall_debug_setup); +#ifdef CONFIG_BOOT_DELAY + +unsigned int boot_delay = 0; /* msecs delay after each printk during bootup */ +extern long preset_lpj; +unsigned long long printk_delay_msec = 0; /* per msec, based on boot_delay */ + +static int __init boot_delay_setup(char *str) +{ + unsigned long lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */ + unsigned long long loops_per_msec = lpj / 1000 * CONFIG_HZ; + + get_option(&str, &boot_delay); + if (boot_delay > 10 * 1000) + boot_delay = 0; + + printk_delay_msec = loops_per_msec; + printk("boot_delay: %u, preset_lpj: %ld, lpj: %lu, CONFIG_HZ: %d, printk_delay_msec: %llu\n", + boot_delay, preset_lpj, lpj, CONFIG_HZ, printk_delay_msec); + + return 1; +} +__setup("boot_delay=", boot_delay_setup); + +#endif + struct task_struct *child_reaper = &init_task; extern initcall_t __initcall_start[], __initcall_end[]; --- linux-2615-work.orig/init/calibrate.c +++ linux-2615-work/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); --- linux-2615-work.orig/kernel/printk.c +++ linux-2615-work/kernel/printk.c @@ -23,6 +23,8 @@ #include <linux/smp_lock.h> #include <linux/console.h> #include <linux/init.h> +#include <linux/jiffies.h> +#include <linux/nmi.h> #include <linux/module.h> #include <linux/interrupt.h> /* For in_interrupt() */ #include <linux/config.h> @@ -201,6 +202,34 @@ out: __setup("log_buf_len=", log_buf_len_setup); +#ifdef CONFIG_BOOT_DELAY + +extern unsigned int boot_delay; /* msecs to delay after each printk during bootup */ +extern long preset_lpj; +extern unsigned long long printk_delay_msec; + +static void boot_delay_msec(int millisecs) +{ + unsigned long long k = printk_delay_msec * millisecs; + unsigned long timeout; + + timeout = jiffies + msecs_to_jiffies(millisecs); + 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(); + } +} + +#endif + /* * Commands to do_syslog: * @@ -520,6 +548,11 @@ asmlinkage int printk(const char *fmt, . r = vprintk(fmt, args); va_end(args); +#ifdef CONFIG_BOOT_DELAY + if (boot_delay && system_state == SYSTEM_BOOTING) + boot_delay_msec(boot_delay); +#endif + return r; } --- linux-2615-work.orig/lib/Kconfig.debug +++ linux-2615-work/lib/Kconfig.debug @@ -186,6 +186,24 @@ config FRAME_POINTER some architectures or if you use external debuggers. If you don't debug the kernel, you can say N. +config BOOT_DELAY + bool "Delay each boot message by N milliseconds" + depends on DEBUG_KERNEL + 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_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