Can jiffies freeze?

[Valdis.Kletnieks at vt.edu]

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).

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