[ltt-dev] Timestamping for ARM

Mathieu Desnoyers compudj at krystal.dyndns.org
Mon Sep 22 12:20:46 EDT 2008

Yeah, generic timestamping in LTTng is just a simple event counter and
does not reflect the time elapsed between events.

Sure, you can use a different time source if your specific ARM board
supports it. It's just a matter of looking at what a patch like
lttng-timestamp-powerpc.patch does for powerpc and do the same for ARM.
You'll probably want to refer to your arch-specific documentation to
find out if you have an high-precision fast time source available which
is synchronised across CPUs.

If you do it correctly (with the right ifdefs and HAVE_* dependency), I
could pull this patch into LTTng so arm boards which have such time
source could have such timing information.

That said, it might be good to extend arch/arm/include/asm/timex.h to
make get_cycles() support your timestamp on your specific board...


* Gaurav Singh (gausinghnsit at gmail.com) wrote:
> Hi,
> I am using an ARM based CPU. Using generic timestamping is giving
> wrong time taken information as it shows most of the time taken in the
> timer inteerupt handler. Is there any other way to present the correct
> timestamping information. As I understand we can use another clock
> source to provide timestamps.
> Regards
> Gaurav Singh
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Mathieu Desnoyers
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