Re: boot_delay broken ?

From: Dave Young
Date: Thu Feb 28 2008 - 03:03:41 EST

On Wed, Feb 27, 2008 at 10:01 AM, Dave Young <hidave.darkstar@xxxxxxxxx> wrote:
>
> On Wed, Feb 27, 2008 at 1:33 AM, Randy Dunlap <randy.dunlap@xxxxxxxxxx> 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@xxxxxxxxx> wrote:
> > > > > On Tue, Feb 26, 2008 at 1:22 PM, Randy Dunlap <randy.dunlap@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx> 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
> >
>
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