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Message-ID: <20070705211346.GB17030@redhat.com>
Date: Thu, 5 Jul 2007 17:13:46 -0400
From: Dave Jones <davej@...hat.com>
To: Linux Kernel <linux-kernel@...r.kernel.org>
Cc: Randy Dunlap <rdunlap@...otime.net>
Subject: slow down printk during boot.
This patch from Randy has proven quite useful from time to time,
and has been in Fedora kernels for a while for that reason.
I fixed up some checkpatch warnings, and rediffed it a bunch
of times, Randy did the heavy lifting.
---
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@...otime.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@...otime.net>
Signed-off-by: Dave Jones <davej@...hat.com>
---
init/calibrate.c | 2 +-
init/main.c | 25 +++++++++++++++++++++++++
kernel/printk.c | 33 +++++++++++++++++++++++++++++++++
lib/Kconfig.debug | 18 ++++++++++++++++++
4 files changed, 77 insertions(+), 1 deletion(-)
--- linux-2.6.19.noarch/init/main.c~ 2006-12-12 09:32:35.000000000 -0500
+++ linux-2.6.19.noarch/init/main.c 2006-12-12 09:33:32.000000000 -0500
@@ -685,6 +685,31 @@ static void __init do_initcalls(void)
flush_scheduled_work();
}
+#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(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);
+
+#endif
+
/*
* Ok, the machine is now initialized. None of the devices
* have been touched yet, but the CPU subsystem is up and
--- 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-2.6.21.noarch/kernel/printk.c~ 2007-05-27 23:01:29.000000000 -0400
+++ linux-2.6.21.noarch/kernel/printk.c 2007-05-27 23:01:37.000000000 -0400
@@ -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() */
@@ -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-2.6.21.noarch/lib/Kconfig.debug~ 2007-05-27 23:02:18.000000000 -0400
+++ linux-2.6.21.noarch/lib/Kconfig.debug 2007-05-27 23:03:14.000000000 -0400
@@ -394,6 +394,24 @@ config FORCED_INLINING
become the default in the future, until then this option is there to
test gcc for this.
+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
--
http://www.codemonkey.org.uk
-
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