The patch titled
printk: add printk_delay to make messages readable for some scenarios
has been added to the -mm tree. Its filename is
printk-add-printk_delay-to-make-messages-readable-for-some-scenarios.patch
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------------------------------------------------------
Subject: printk: add printk_delay to make messages readable for some scenarios
From: Dave Young <hidave.darkstar@xxxxxxxxx>
When syslog is not possible, at the same time there's no serial/net
console available, it will be hard to read the printk messages. For
example oops/panic/warning messages in shutdown phase.
Add a printk delay feature, we can make each printk message delay some
milliseconds.
Setting the delay by proc/sysctl interface: /proc/sys/kernel/printk_delay
The value range from 0 - 10000, default value is 0
Signed-off-by: Dave Young <hidave.darkstar@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/sysctl/kernel.txt | 8 ++++++++
include/linux/kernel.h | 2 ++
include/linux/sysctl.h | 1 +
kernel/printk.c | 14 ++++++++++++++
kernel/sysctl.c | 12 ++++++++++++
5 files changed, 37 insertions(+)
diff -puN Documentation/sysctl/kernel.txt~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios Documentation/sysctl/kernel.txt
--- a/Documentation/sysctl/kernel.txt~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios
+++ a/Documentation/sysctl/kernel.txt
@@ -297,6 +297,14 @@ send before ratelimiting kicks in.
==============================================================
+printk_delay:
+
+Delay each printk message in printk_delay milliseconds
+
+Value from 0 - 10000 is allowed.
+
+==============================================================
+
randomize-va-space:
This option can be used to select the type of process address
diff -puN include/linux/kernel.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios include/linux/kernel.h
--- a/include/linux/kernel.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios
+++ a/include/linux/kernel.h
@@ -245,6 +245,8 @@ extern int printk_ratelimit(void);
extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
unsigned int interval_msec);
+extern int printk_delay_msec;
+
/*
* Print a one-time message (analogous to WARN_ONCE() et al):
*/
diff -puN include/linux/sysctl.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios include/linux/sysctl.h
--- a/include/linux/sysctl.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios
+++ a/include/linux/sysctl.h
@@ -163,6 +163,7 @@ enum
KERN_MAX_LOCK_DEPTH=74,
KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */
KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */
+ KERN_PRINTK_DELAY = 77, /* int: tune printk delay*/
};
diff -puN kernel/printk.c~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios kernel/printk.c
--- a/kernel/printk.c~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios
+++ a/kernel/printk.c
@@ -640,6 +640,19 @@ static int recursion_bug;
static int new_text_line = 1;
static char printk_buf[1024];
+int printk_delay_msec;
+
+static inline void printk_delay(void)
+{
+ if (unlikely(printk_delay_msec)) {
+ int m = printk_delay_msec;
+ while (m--) {
+ mdelay(1);
+ touch_nmi_watchdog();
+ }
+ }
+}
+
asmlinkage int vprintk(const char *fmt, va_list args)
{
int printed_len = 0;
@@ -649,6 +662,7 @@ asmlinkage int vprintk(const char *fmt,
char *p;
boot_delay_msec();
+ printk_delay();
preempt_disable();
/* This stops the holder of console_sem just where we want him */
diff -puN kernel/sysctl.c~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios kernel/sysctl.c
--- a/kernel/sysctl.c~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios
+++ a/kernel/sysctl.c
@@ -103,6 +103,7 @@ static int __maybe_unused one = 1;
static int __maybe_unused two = 2;
static unsigned long one_ul = 1;
static int one_hundred = 100;
+static int ten_thousand = 10000;
/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
static unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
@@ -708,6 +709,17 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = KERN_PRINTK_DELAY,
+ .procname = "printk_delay",
+ .data = &printk_delay_msec,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec_minmax,
+ .strategy = &sysctl_intvec,
+ .extra1 = &zero,
+ .extra2 = &ten_thousand,
+ },
#endif
{
.ctl_name = KERN_NGROUPS_MAX,
_
Patches currently in -mm which might be from hidave.darkstar@xxxxxxxxx are
origin.patch
printk-add-printk_delay-to-make-messages-readable-for-some-scenarios.patch
printk-add-printk_delay-to-make-messages-readable-for-some-scenarios-fix.patch
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