The patch titled
slow down printk during boot
has been added to the -mm tree. Its filename is
slow-down-printk-during-boot.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: slow down printk during boot
From: Randy Dunlap <rdunlap@xxxxxxxxxxxx>
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.
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxx>
Signed-off-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/kernel-parameters.txt | 5 ++
include/linux/jiffies.h | 2 +
init/calibrate.c | 2 -
kernel/printk.c | 51 ++++++++++++++++++++++++++
lib/Kconfig.debug | 18 +++++++++
5 files changed, 77 insertions(+), 1 deletion(-)
diff -puN Documentation/kernel-parameters.txt~slow-down-printk-during-boot Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~slow-down-printk-during-boot
+++ a/Documentation/kernel-parameters.txt
@@ -345,6 +345,11 @@ and is between 256 and 4096 characters.
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 -puN include/linux/jiffies.h~slow-down-printk-during-boot include/linux/jiffies.h
--- a/include/linux/jiffies.h~slow-down-printk-during-boot
+++ a/include/linux/jiffies.h
@@ -150,6 +150,8 @@ 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 -puN init/calibrate.c~slow-down-printk-during-boot init/calibrate.c
--- a/init/calibrate.c~slow-down-printk-during-boot
+++ a/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 -puN kernel/printk.c~slow-down-printk-during-boot kernel/printk.c
--- a/kernel/printk.c~slow-down-printk-during-boot
+++ a/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 +164,50 @@ out:
__setup("log_buf_len=", log_buf_len_setup);
+#ifdef CONFIG_BOOT_PRINTK_DELAY
+
+unsigned int boot_delay; /* msecs delay after each printk during bootup */
+unsigned long long printk_delay_msec; /* 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(KERN_DEBUG "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);
+
+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:
*
@@ -513,6 +559,11 @@ asmlinkage int printk(const char *fmt, .
r = vprintk(fmt, args);
va_end(args);
+#ifdef CONFIG_BOOT_PRINTK_DELAY
+ if (boot_delay && system_state == SYSTEM_BOOTING)
+ boot_delay_msec(boot_delay);
+#endif
+
return r;
}
diff -puN lib/Kconfig.debug~slow-down-printk-during-boot lib/Kconfig.debug
--- a/lib/Kconfig.debug~slow-down-printk-during-boot
+++ a/lib/Kconfig.debug
@@ -418,6 +418,24 @@ 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
+ 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
_
Patches currently in -mm which might be from rdunlap@xxxxxxxxxxxx are
x86_64-pm_trace-support.patch
ext3-ext4-orphan-list-check-on-destroy_inode.patch
update-procfs-guide-doc-of-read_func.patch
slow-down-printk-during-boot.patch
crc7-support.patch
coredump-masking-documentation-for-proc-pid-coredump_filter.patch
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