Can jiffies freeze?

[sandeep kumar]

Hi Valdis,
Device specs: CPU: 1.7Ghz & RAM: 2GB.
We are not adding any code in the mm_init, All we do is reserve some memory
during the boot time and rest of the memory around 1.45GB we configure it
as HIGHMEM.

Can you give me any info on how to do the profiling of the function calls
during ealry booting in the kernel.

Thanks
Sandeep


On Tue, Jan 22, 2013 at 12:38 PM, <Valdis.Kletnieks at vt.edu> wrote:

> On Tue, 22 Jan 2013 11:32:19 -0800, sandeep kumar said:
>
> > as you rightly mentioned,cat /proc/kmsg is showing the time stamps,
> > according to that it is 0ms only.
> > But when you see the same with UART there is 2sec delay in showing the
> next
> > log. i caught this while i m observing the UART logs with
> > "Terminaliranicca".
>
> Oh, I could believe there's 2 seconds of time used up there that doesn't
> show in kernel timestamps because the timers aren't started yet.
>
> > Since i m early in the mm_init, i cant use watchdog to detect it,
> hrtimers
> > i cant use..i am really thinking how to analyse this delay..
>
> Time for some lateral thinking.. :)
>
> Can you give us some specs on the hardware (in particular, the CPU
> type/speed
> and how much RAM is installed)?  2 seconds on a 2Ghz CPU is about 4 billion
> cycles.
>
> Also, are you adding any code into the mm_init path? If so, what exactly
> are you doing?
>
> I wonder how early the kernel tracing and profiling stuff is enabled.  It
> may
> be possible to boot a kernel that has function-call tracing enabled, which
> would not have timing info, but if you see a function that's being called
> 500K
> times that should only be called a dozen times, that's probably your
> problem :)
> You'd probably want it with 'init=/bin/bash' and dump the stuff, as
> running to
> multiuser will almost certainly roll the buffers and lose the info).
>
>


-- 
With regards,
Sandeep Kumar Anantapalli,
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