boot_delay broken ?

boot_delay broken ?

[Dave Jones]

The boot_delay switch seems to be behaving strangely in the
current -git.  Setting it to =10 makes the output 'bursty'
it becomes slow for some printk's whilst others scroll by
at regular speed.
Setting it any higher than that seems to make it pause for
a really long time before it outputs any text at all.

x86 timer changes perhaps ?

	Dave

-- 
http://www.codemonkey.org.uk

Re: boot_delay broken ?

[Dave Young]

On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
> The boot_delay switch seems to be behaving strangely in the
>  current -git.  Setting it to =10 makes the output 'bursty'
>  it becomes slow for some printk's whilst others scroll by
>  at regular speed.
>  Setting it any higher than that seems to make it pause for
>  a really long time before it outputs any text at all.

On my side there's this issue for a long time
http://lkml.org/lkml/2007/8/8/79

>
>  x86 timer changes perhaps ?
>
>         Dave
>
>  --
>  http://www.codemonkey.org.uk
>  --
>  To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>  the body of a message to majordomo@vger.kernel.org
>  More majordomo info at  http://vger.kernel.org/majordomo-info.html
>  Please read the FAQ at  http://www.tux.org/lkml/
>

Re: boot_delay broken ?

[Randy Dunlap]

On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:

> On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
> > The boot_delay switch seems to be behaving strangely in the
> >  current -git.  Setting it to =10 makes the output 'bursty'
> >  it becomes slow for some printk's whilst others scroll by
> >  at regular speed.
> >  Setting it any higher than that seems to make it pause for
> >  a really long time before it outputs any text at all.
> 
> On my side there's this issue for a long time
> http://lkml.org/lkml/2007/8/8/79

[http://marc.info/?l=linux-kernel&m=118655896515049&w=2]

You asked questions and they were answered.  Perhaps you didn't like
the answers.

Here's a question for you.  What kernel boot options did you use?
Specifically, for lpj= and boot_delay= ?

> >
> >  x86 timer changes perhaps ?


---
~Randy

Re: boot_delay broken ?

[Dave Young]

On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
> On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
>
>  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
>  > > The boot_delay switch seems to be behaving strangely in the
>  > >  current -git.  Setting it to =10 makes the output 'bursty'
>  > >  it becomes slow for some printk's whilst others scroll by
>  > >  at regular speed.
>  > >  Setting it any higher than that seems to make it pause for
>  > >  a really long time before it outputs any text at all.
>  >
>  > On my side there's this issue for a long time
>  > http://lkml.org/lkml/2007/8/8/79
>
>  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
>
>  You asked questions and they were answered.  Perhaps you didn't like
>  the answers.

No, I like it.  Thanks.

But I still want to know why mdelay can not be used.
is it not available for all archs or something else?

>
>  Here's a question for you.  What kernel boot options did you use?
>  Specifically, for lpj= and boot_delay= ?

I tried boot_delay=100 and boot_delay=200 without lpj set, The result
was really slow. It was better with lpj copied from dmesg, but was
still slower then mdelay.

I think we can firstly use preset lpj, after delay calibrating just
use the system lpj

>
>  > >
>  > >  x86 timer changes perhaps ?
>
>
>  ---
>  ~Randy
>

Re: boot_delay broken ?

[Dave Young]

On Tue, Feb 26, 2008 at 1:48 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
> On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
>  > On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
>  >
>  >  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
>  >  > > The boot_delay switch seems to be behaving strangely in the
>  >  > >  current -git.  Setting it to =10 makes the output 'bursty'
>  >  > >  it becomes slow for some printk's whilst others scroll by
>  >  > >  at regular speed.
>  >  > >  Setting it any higher than that seems to make it pause for
>  >  > >  a really long time before it outputs any text at all.
>  >  >
>  >  > On my side there's this issue for a long time
>  >  > http://lkml.org/lkml/2007/8/8/79
>  >
>  >  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
>  >
>  >  You asked questions and they were answered.  Perhaps you didn't like
>  >  the answers.
>
>  No, I like it.  Thanks.
>
>  But I still want to know why mdelay can not be used.
>  is it not available for all archs or something else?
>
>
>  >
>  >  Here's a question for you.  What kernel boot options did you use?
>  >  Specifically, for lpj= and boot_delay= ?
>
>  I tried boot_delay=100 and boot_delay=200 without lpj set, The result
>  was really slow. It was better with lpj copied from dmesg, but was
>  still slower then mdelay.

Especially at the very beginning after the message "Booting the kernel",
I need to wait several minutes to see the afterwards messages

>
>  I think we can firstly use preset lpj, after delay calibrating just
>  use the system lpj
>
>
>
>  >
>  >  > >
>  >  > >  x86 timer changes perhaps ?
>  >
>  >
>  >  ---
>  >  ~Randy
>  >
>

Re: boot_delay broken ?

[Dave Young]

On Tue, Feb 26, 2008 at 01:59:31PM +0800, Dave Young wrote:
> On Tue, Feb 26, 2008 at 1:48 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
> > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
> >  > On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
> >  >
> >  >  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
> >  >  > > The boot_delay switch seems to be behaving strangely in the
> >  >  > >  current -git.  Setting it to =10 makes the output 'bursty'
> >  >  > >  it becomes slow for some printk's whilst others scroll by
> >  >  > >  at regular speed.
> >  >  > >  Setting it any higher than that seems to make it pause for
> >  >  > >  a really long time before it outputs any text at all.
> >  >  >
> >  >  > On my side there's this issue for a long time
> >  >  > http://lkml.org/lkml/2007/8/8/79
> >  >
> >  >  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
> >  >
> >  >  You asked questions and they were answered.  Perhaps you didn't like
> >  >  the answers.
> >
> >  No, I like it.  Thanks.
> >
> >  But I still want to know why mdelay can not be used.
> >  is it not available for all archs or something else?
> >
> >
> >  >
> >  >  Here's a question for you.  What kernel boot options did you use?
> >  >  Specifically, for lpj= and boot_delay= ?
> >
> >  I tried boot_delay=100 and boot_delay=200 without lpj set, The result
> >  was really slow. It was better with lpj copied from dmesg, but was
> >  still slower then mdelay.
> 
> Especially at the very beginning after the message "Booting the kernel",
> I need to wait several minutes to see the afterwards messages
> 
> >
> >  I think we can firstly use preset lpj, after delay calibrating just
> >  use the system lpj
> >
> >
> >
> >  >
> >  >  > >
> >  >  > >  x86 timer changes perhaps ?
> >  >
> >  >
> >  >  ---
> >  >  ~Randy
> >  >
> >

How about use loops_per_jiffy as following? With this patch at least
for me the very long delay at the very begining does not occur.

kernel/printk.c |   15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)

diff -upr linux/kernel/printk.c linux.new/kernel/printk.c
--- linux/kernel/printk.c	2008-02-26 16:54:23.000000000 +0800
+++ linux.new/kernel/printk.c	2008-02-26 16:59:02.000000000 +0800
@@ -173,24 +173,14 @@ __setup("log_buf_len=", log_buf_len_setu
 #ifdef CONFIG_BOOT_PRINTK_DELAY
 
 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
-static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 
 static int __init boot_delay_setup(char *str)
 {
-	unsigned long lpj;
-	unsigned long long loops_per_msec;
-
-	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
-	loops_per_msec = (unsigned long long)lpj / 1000 * 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, "
-		"HZ: %d, printk_delay_msec: %llu\n",
-		boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
+	printk(KERN_DEBUG "boot_delay: %u\n", boot_delay);
 	return 1;
 }
 __setup("boot_delay=", boot_delay_setup);
@@ -199,6 +189,9 @@ static void boot_delay_msec(void)
 {
 	unsigned long long k;
 	unsigned long timeout;
+	unsigned long long printk_delay_msec;
+
+	printk_delay_msec = (unsigned long long)loops_per_jiffy / 1000 * HZ;
 
 	if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 		return;

Re: boot_delay broken ?

[Randy Dunlap]

On Tue, 26 Feb 2008 17:09:48 +0800 Dave Young wrote:

> On Tue, Feb 26, 2008 at 01:59:31PM +0800, Dave Young wrote:
> > On Tue, Feb 26, 2008 at 1:48 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
> > > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
> > >  > On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
> > >  >
> > >  >  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
> > >  >  > > The boot_delay switch seems to be behaving strangely in the
> > >  >  > >  current -git.  Setting it to =10 makes the output 'bursty'
> > >  >  > >  it becomes slow for some printk's whilst others scroll by
> > >  >  > >  at regular speed.
> > >  >  > >  Setting it any higher than that seems to make it pause for
> > >  >  > >  a really long time before it outputs any text at all.
> > >  >  >
> > >  >  > On my side there's this issue for a long time
> > >  >  > http://lkml.org/lkml/2007/8/8/79
> > >  >
> > >  >  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
> > >  >
> > >  >  You asked questions and they were answered.  Perhaps you didn't like
> > >  >  the answers.
> > >
> > >  No, I like it.  Thanks.
> > >
> > >  But I still want to know why mdelay can not be used.
> > >  is it not available for all archs or something else?
> > >
> > >
> > >  >
> > >  >  Here's a question for you.  What kernel boot options did you use?
> > >  >  Specifically, for lpj= and boot_delay= ?
> > >
> > >  I tried boot_delay=100 and boot_delay=200 without lpj set, The result
> > >  was really slow. It was better with lpj copied from dmesg, but was
> > >  still slower then mdelay.
> > 
> > Especially at the very beginning after the message "Booting the kernel",
> > I need to wait several minutes to see the afterwards messages
> > 
> > >
> > >  I think we can firstly use preset lpj, after delay calibrating just
> > >  use the system lpj
> > >
> > >
> > >
> > >  >
> > >  >  > >
> > >  >  > >  x86 timer changes perhaps ?
> > >  >
> > >  >
> > >  >  ---
> > >  >  ~Randy
> > >  >
> > >
> 
> How about use loops_per_jiffy as following? With this patch at least
> for me the very long delay at the very begining does not occur.
> 
> kernel/printk.c |   15 ++++-----------
> 1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff -upr linux/kernel/printk.c linux.new/kernel/printk.c
> --- linux/kernel/printk.c	2008-02-26 16:54:23.000000000 +0800
> +++ linux.new/kernel/printk.c	2008-02-26 16:59:02.000000000 +0800
> @@ -173,24 +173,14 @@ __setup("log_buf_len=", log_buf_len_setu
>  #ifdef CONFIG_BOOT_PRINTK_DELAY
>  
>  static unsigned int boot_delay; /* msecs delay after each printk during bootup */
> -static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
>  
>  static int __init boot_delay_setup(char *str)
>  {
> -	unsigned long lpj;
> -	unsigned long long loops_per_msec;
> -
> -	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
> -	loops_per_msec = (unsigned long long)lpj / 1000 * 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, "
> -		"HZ: %d, printk_delay_msec: %llu\n",
> -		boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
> +	printk(KERN_DEBUG "boot_delay: %u\n", boot_delay);
>  	return 1;
>  }
>  __setup("boot_delay=", boot_delay_setup);
> @@ -199,6 +189,9 @@ static void boot_delay_msec(void)
>  {
>  	unsigned long long k;
>  	unsigned long timeout;
> +	unsigned long long printk_delay_msec;
> +
> +	printk_delay_msec = (unsigned long long)loops_per_jiffy / 1000 * HZ;
>  
>  	if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
>  		return;
> --

Hi Dave,

That might work, but IMO it requires someone to audit all
architectures to make sure that loops_per_jiffy has been calibrated
at that point in time (as I mentioned in http://lkml.org/lkml/2007/8/11/153).

I didn't do that and you said that you tested i386 only.

Maybe you can get Andrew to merge it into -mm for testing...

However, setting boot_delay=N without setting lpj=M is just not
advisable.  The Kconfig help text for BOOT_PRINTK_DELAY tries to
say that.  Maybe it needs to be stronger?

	  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".


---
~Randy

Re: boot_delay broken ?

[Dave Young]

On Wed, Feb 27, 2008 at 1:33 AM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
>
> On Tue, 26 Feb 2008 17:09:48 +0800 Dave Young wrote:
>
>  > On Tue, Feb 26, 2008 at 01:59:31PM +0800, Dave Young wrote:
>  > > On Tue, Feb 26, 2008 at 1:48 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
>  > > > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
>  > > >  > On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
>  > > >  >
>  > > >  >  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
>  > > >  >  > > The boot_delay switch seems to be behaving strangely in the
>  > > >  >  > >  current -git.  Setting it to =10 makes the output 'bursty'
>  > > >  >  > >  it becomes slow for some printk's whilst others scroll by
>  > > >  >  > >  at regular speed.
>  > > >  >  > >  Setting it any higher than that seems to make it pause for
>  > > >  >  > >  a really long time before it outputs any text at all.
>  > > >  >  >
>  > > >  >  > On my side there's this issue for a long time
>  > > >  >  > http://lkml.org/lkml/2007/8/8/79
>  > > >  >
>  > > >  >  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
>  > > >  >
>  > > >  >  You asked questions and they were answered.  Perhaps you didn't like
>  > > >  >  the answers.
>  > > >
>  > > >  No, I like it.  Thanks.
>  > > >
>  > > >  But I still want to know why mdelay can not be used.
>  > > >  is it not available for all archs or something else?
>  > > >
>  > > >
>  > > >  >
>  > > >  >  Here's a question for you.  What kernel boot options did you use?
>  > > >  >  Specifically, for lpj= and boot_delay= ?
>  > > >
>  > > >  I tried boot_delay=100 and boot_delay=200 without lpj set, The result
>  > > >  was really slow. It was better with lpj copied from dmesg, but was
>  > > >  still slower then mdelay.
>  > >
>  > > Especially at the very beginning after the message "Booting the kernel",
>  > > I need to wait several minutes to see the afterwards messages
>  > >
>  > > >
>  > > >  I think we can firstly use preset lpj, after delay calibrating just
>  > > >  use the system lpj
>  > > >
>  > > >
>  > > >
>  > > >  >
>  > > >  >  > >
>  > > >  >  > >  x86 timer changes perhaps ?
>  > > >  >
>  > > >  >
>  > > >  >  ---
>  > > >  >  ~Randy
>  > > >  >
>  > > >
>  >
>  > How about use loops_per_jiffy as following? With this patch at least
>  > for me the very long delay at the very begining does not occur.
>  >
>  > kernel/printk.c |   15 ++++-----------
>  > 1 file changed, 4 insertions(+), 11 deletions(-)
>  >
>  > diff -upr linux/kernel/printk.c linux.new/kernel/printk.c
>  > --- linux/kernel/printk.c     2008-02-26 16:54:23.000000000 +0800
>  > +++ linux.new/kernel/printk.c 2008-02-26 16:59:02.000000000 +0800
>  > @@ -173,24 +173,14 @@ __setup("log_buf_len=", log_buf_len_setu
>  >  #ifdef CONFIG_BOOT_PRINTK_DELAY
>  >
>  >  static unsigned int boot_delay; /* msecs delay after each printk during bootup */
>  > -static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
>  >
>  >  static int __init boot_delay_setup(char *str)
>  >  {
>  > -     unsigned long lpj;
>  > -     unsigned long long loops_per_msec;
>  > -
>  > -     lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
>  > -     loops_per_msec = (unsigned long long)lpj / 1000 * 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, "
>  > -             "HZ: %d, printk_delay_msec: %llu\n",
>  > -             boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
>  > +     printk(KERN_DEBUG "boot_delay: %u\n", boot_delay);
>  >       return 1;
>  >  }
>  >  __setup("boot_delay=", boot_delay_setup);
>  > @@ -199,6 +189,9 @@ static void boot_delay_msec(void)
>  >  {
>  >       unsigned long long k;
>  >       unsigned long timeout;
>  > +     unsigned long long printk_delay_msec;
>  > +
>  > +     printk_delay_msec = (unsigned long long)loops_per_jiffy / 1000 * HZ;
>  >
>  >       if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
>  >               return;
>  > --
>
>  Hi Dave,
>
>  That might work, but IMO it requires someone to audit all
>  architectures to make sure that loops_per_jiffy has been calibrated
>  at that point in time
>(as I mentioned in http://lkml.org/lkml/2007/8/11/153).

Sorry for missing your words about this.

>
>  I didn't do that and you said that you tested i386 only.
>
>  Maybe you can get Andrew to merge it into -mm for testing...

Andrew, what's your opinon?

>
>  However, setting boot_delay=N without setting lpj=M is just not
>  advisable.  The Kconfig help text for BOOT_PRINTK_DELAY tries to
>  say that.  Maybe it needs to be stronger?

I think it's enough now.

I tested boot_delay yestoday, and found the result is different with
before version.
Even with lpj preset the delay is very slow, 5-10 seconds for every printk.
Maybe this is what davej said.

I will do some more test and hack about this today.

>
>           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".
>
>
>  ---
>  ~Randy
>

Re: boot_delay broken ?

[Pavel Machek]

On Sat 2008-02-23 19:46:15, Dave Jones wrote:
> The boot_delay switch seems to be behaving strangely in the
> current -git.  Setting it to =10 makes the output 'bursty'
> it becomes slow for some printk's whilst others scroll by
> at regular speed.
> Setting it any higher than that seems to make it pause for
> a really long time before it outputs any text at all.
> 
> x86 timer changes perhaps ?

If nohz=off highres=off notsc fixes it, it is probably timers :-).


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: boot_delay broken ?

[Dave Young]

On Wed, Feb 27, 2008 at 10:01 AM, Dave Young <hidave.darkstar@gmail.com> wrote:
>
> On Wed, Feb 27, 2008 at 1:33 AM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
>  >
>  > On Tue, 26 Feb 2008 17:09:48 +0800 Dave Young wrote:
>  >
>  >  > On Tue, Feb 26, 2008 at 01:59:31PM +0800, Dave Young wrote:
>  >  > > On Tue, Feb 26, 2008 at 1:48 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
>  >  > > > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@oracle.com> wrote:
>  >  > > >  > On Mon, 25 Feb 2008 10:14:36 +0800 Dave Young wrote:
>  >  > > >  >
>  >  > > >  >  > On Sun, Feb 24, 2008 at 8:46 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
>  >  > > >  >  > > The boot_delay switch seems to be behaving strangely in the
>  >  > > >  >  > >  current -git.  Setting it to =10 makes the output 'bursty'
>  >  > > >  >  > >  it becomes slow for some printk's whilst others scroll by
>  >  > > >  >  > >  at regular speed.
>  >  > > >  >  > >  Setting it any higher than that seems to make it pause for
>  >  > > >  >  > >  a really long time before it outputs any text at all.
>  >  > > >  >  >
>  >  > > >  >  > On my side there's this issue for a long time
>  >  > > >  >  > http://lkml.org/lkml/2007/8/8/79
>  >  > > >  >
>  >  > > >  >  [http://marc.info/?l=linux-kernel&m=118655896515049&w=2]
>  >  > > >  >
>  >  > > >  >  You asked questions and they were answered.  Perhaps you didn't like
>  >  > > >  >  the answers.
>  >  > > >
>  >  > > >  No, I like it.  Thanks.
>  >  > > >
>  >  > > >  But I still want to know why mdelay can not be used.
>  >  > > >  is it not available for all archs or something else?
>  >  > > >
>  >  > > >
>  >  > > >  >
>  >  > > >  >  Here's a question for you.  What kernel boot options did you use?
>  >  > > >  >  Specifically, for lpj= and boot_delay= ?
>  >  > > >
>  >  > > >  I tried boot_delay=100 and boot_delay=200 without lpj set, The result
>  >  > > >  was really slow. It was better with lpj copied from dmesg, but was
>  >  > > >  still slower then mdelay.
>  >  > >
>  >  > > Especially at the very beginning after the message "Booting the kernel",
>  >  > > I need to wait several minutes to see the afterwards messages

Answer to myself : It's due to the first delayed printk.

>  >  > >
>  >  > > >
>  >  > > >  I think we can firstly use preset lpj, after delay calibrating just
>  >  > > >  use the system lpj
>  >  > > >
>  >  > > >
>  >  > > >
>  >  > > >  >
>  >  > > >  >  > >
>  >  > > >  >  > >  x86 timer changes perhaps ?
>  >  > > >  >
>  >  > > >  >
>  >  > > >  >  ---
>  >  > > >  >  ~Randy
>  >  > > >  >
>  >  > > >
>  >  >
>  >  > How about use loops_per_jiffy as following? With this patch at least
>  >  > for me the very long delay at the very begining does not occur.

It does impoving the code, but does not resolve problem here.

It looks ok because the loops_per_jiffy initial value is 4096, with
this value the delay result is much better than with values copied
from calibrated results.

BTW, Pavel's suggest (nohz=off highres=off notsc) does not help me.

>  >  >
>  >  > kernel/printk.c |   15 ++++-----------
>  >  > 1 file changed, 4 insertions(+), 11 deletions(-)
>  >  >
>  >  > diff -upr linux/kernel/printk.c linux.new/kernel/printk.c
>  >  > --- linux/kernel/printk.c     2008-02-26 16:54:23.000000000 +0800
>  >  > +++ linux.new/kernel/printk.c 2008-02-26 16:59:02.000000000 +0800
>  >  > @@ -173,24 +173,14 @@ __setup("log_buf_len=", log_buf_len_setu
>  >  >  #ifdef CONFIG_BOOT_PRINTK_DELAY
>  >  >
>  >  >  static unsigned int boot_delay; /* msecs delay after each printk during bootup */
>  >  > -static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
>  >  >
>  >  >  static int __init boot_delay_setup(char *str)
>  >  >  {
>  >  > -     unsigned long lpj;
>  >  > -     unsigned long long loops_per_msec;
>  >  > -
>  >  > -     lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
>  >  > -     loops_per_msec = (unsigned long long)lpj / 1000 * 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, "
>  >  > -             "HZ: %d, printk_delay_msec: %llu\n",
>  >  > -             boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
>  >  > +     printk(KERN_DEBUG "boot_delay: %u\n", boot_delay);
>  >  >       return 1;
>  >  >  }
>  >  >  __setup("boot_delay=", boot_delay_setup);
>  >  > @@ -199,6 +189,9 @@ static void boot_delay_msec(void)
>  >  >  {
>  >  >       unsigned long long k;
>  >  >       unsigned long timeout;
>  >  > +     unsigned long long printk_delay_msec;
>  >  > +
>  >  > +     printk_delay_msec = (unsigned long long)loops_per_jiffy / 1000 * HZ;
>  >  >
>  >  >       if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
>  >  >               return;
>  >  > --
>  >
>  >  Hi Dave,
>  >
>  >  That might work, but IMO it requires someone to audit all
>  >  architectures to make sure that loops_per_jiffy has been calibrated
>  >  at that point in time
>  >(as I mentioned in http://lkml.org/lkml/2007/8/11/153).
>
>  Sorry for missing your words about this.
>
>
>  >
>  >  I didn't do that and you said that you tested i386 only.
>  >
>  >  Maybe you can get Andrew to merge it into -mm for testing...
>
>  Andrew, what's your opinon?
>
>
>  >
>  >  However, setting boot_delay=N without setting lpj=M is just not
>  >  advisable.  The Kconfig help text for BOOT_PRINTK_DELAY tries to
>  >  say that.  Maybe it needs to be stronger?
>
>  I think it's enough now.
>
>  I tested boot_delay yestoday, and found the result is different with
>  before version.
>  Even with lpj preset the delay is very slow, 5-10 seconds for every printk.
>  Maybe this is what davej said.
>
>  I will do some more test and hack about this today.
>
>
>
>  >
>  >           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".
>  >
>  >
>  >  ---
>  >  ~Randy
>  >
>