Message-Id: <20080226093323.71ae516b.randy.dunlap@oracle.com>
Date:	Tue, 26 Feb 2008 09:33:23 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	akpm <akpm@...ux-foundation.org>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: boot_delay broken ?

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@...il.com> wrote:
> > > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@...cle.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@...emonkey.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
--
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