diff options
| author | Randy Dunlap <rdunlap@xenotime.net> | 2007-10-16 01:23:46 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-10-16 09:42:49 -0700 |
| commit | bfe8df3d314bddf30758bd738e0087e80964760c (patch) | |
| tree | d04db4fb2592e2d416073681903f05f5b30f204b /lib | |
| parent | 1bcf548293aef19b0797348332cf1dfbf2116cef (diff) | |
| download | lwn-bfe8df3d314bddf30758bd738e0087e80964760c.tar.gz lwn-bfe8df3d314bddf30758bd738e0087e80964760c.zip | |
slow down printk during boot
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_PRINTK_DELAY=y and then add (e.g.):
"lpj=loops_per_jiffy boot_delay=100"
to the kernel command line.
It has been useful in cases like "during boot, my machine just reboots or the
screen goes black" by slowing down printk, (and adding initcall_debug), we can
usually see the last thing that happened before the lights went out which is
usually a valuable clue.
[akpm@linux-foundation.org: not all architectures implement CONFIG_HZ]
[akpm@linux-foundation.org: fix lots of stuff]
[bunk@stusta.de: kernel/printk.c: make 2 variables static]
[heiko.carstens@de.ibm.com: fix slow down printk on boot compile error]
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig.debug | 18 |
1 files changed, 18 insertions, 0 deletions
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 |