linux-kernel - Re: boot

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Message-ID: <20080226090948.GA2794@darkstar.te-china.tietoenator.com>
Date:	Tue, 26 Feb 2008 17:09:48 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Randy Dunlap <randy.dunlap@...cle.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, 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;
--
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