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Date: Tue, 23 Jun 2009 20:36:41 +0800
From: Dave Young <hidave.darkstar@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] printk: add printk_delay to make messages readable for
some scenarios
On Mon, Jun 22, 2009 at 10:51:54PM -0700, Andrew Morton wrote:
> On Tue, 16 Jun 2009 16:54:12 +0800 Dave Young <hidave.darkstar@...il.com> wrote:
>
> > 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.
> >
> > Here 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
> >
>
> Seems OK(ish).
>
> > ---
> > 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(+)
> >
> > --- linux-2.6.orig/kernel/printk.c 2009-06-16 11:07:15.000000000 +0800
> > +++ linux-2.6/kernel/printk.c 2009-06-16 11:31:01.000000000 +0800
> > @@ -638,6 +638,19 @@ 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;
> > @@ -647,6 +660,7 @@ 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 */
> > --- linux-2.6.orig/include/linux/kernel.h 2009-04-18 19:48:06.000000000 +0800
> > +++ linux-2.6/include/linux/kernel.h 2009-06-16 11:24:43.000000000 +0800
> > @@ -243,6 +243,8 @@ extern int printk_ratelimit(void);
> > extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
> > unsigned int interval_msec);
> >
> > +extern int printk_delay_msec;
> > +
>
> Sigh.
>
> It's pretty dumb to clutter up kernel.h just because we want to share a
> declaration with sysctl.c. And it was pretty dumb to fill sysctl.c with
> extern declarations.
>
> What we should do is to create a new header file which contains all the
> declarations which sysctl.c needs. Include that from within sysctl.c
> and all .c files which which to share declarations with sysctl.c.
>
> But that's all a matter for another patchset.
>
Should do, thanks for pointing out.
> > /*
> > * Print a one-time message (analogous to WARN_ONCE() et al):
> > */
> > --- linux-2.6.orig/kernel/sysctl.c 2009-06-15 10:33:11.000000000 +0800
> > +++ linux-2.6/kernel/sysctl.c 2009-06-16 11:29:52.000000000 +0800
> > @@ -102,6 +102,7 @@ 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;
> > @@ -699,6 +700,17 @@ 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
>
> See that endif there? If CONFIG_PRINTK=n, we'll get an unused-var
> warning for `ten_thousand'. Another sysctl.c wart. I'll fix it.
Yes, thanks very much.
>
> > {
> > .ctl_name = KERN_NGROUPS_MAX,
> > --- linux-2.6.orig/include/linux/sysctl.h 2009-04-09 16:23:01.000000000 +0800
> > +++ linux-2.6/include/linux/sysctl.h 2009-06-16 12:30:14.000000000 +0800
> > @@ -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*/
>
> No, we don't do this any more. I'll fix that too.
>
> Please retest the result.
Tested, thanks.
>
>
> diff -puN include/linux/sysctl.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios-fix include/linux/sysctl.h
> --- a/include/linux/sysctl.h~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios-fix
> +++ a/include/linux/sysctl.h
> @@ -163,7 +163,6 @@ 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*/
> };
>
>
> --- a/kernel/sysctl.c~printk-add-printk_delay-to-make-messages-readable-for-some-scenarios-fix
> +++ a/kernel/sysctl.c
> @@ -103,7 +103,9 @@ static int __maybe_unused one = 1;
> static int __maybe_unused two = 2;
> static unsigned long one_ul = 1;
> static int one_hundred = 100;
> +#ifdef CONFIG_PRINTK
> static int ten_thousand = 10000;
> +#endif
>
> /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
> static unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
> @@ -710,7 +712,7 @@ static struct ctl_table kern_table[] = {
> .proc_handler = &proc_dointvec,
> },
> {
> - .ctl_name = KERN_PRINTK_DELAY,
> + .ctl_name = CTL_UNNUMBERED,
> .procname = "printk_delay",
> .data = &printk_delay_msec,
> .maxlen = sizeof(int),
> _
>
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