[ltt-dev] Timestamping for ARM

[gausinghnsit@gmail.com (Gaurav Singh)]

Hi Matheiu/All,

I have managed to supply a timer to LTTng on my ST Nomadik (ARM based
chip) 8815 board. Luckily there are timers that I can use.
I am using another custom designed tool to find times for interrupt
handlers and bottom halves. After using the new timer for timestamping
I am getting similar results in LTT which probably proves the working
of the method.
However are there any other tests I can use to verify the working?
Also interrupt handler times are wrong using the LTTV version
(lttv-0.10.0-pre11-10032008). The patch supplied earlier is giving me
the correct times. Is the patch correct? What is the status of the
Interrupt handler time plugin in LTTV? I see that I have to load it
seperately - does that mean it is not fully supported?


Regards
Gaurav

On Mon, Sep 22, 2008 at 9:50 PM, Mathieu Desnoyers
<compudj at krystal.dyndns.org> wrote:
> 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...
>
> Mathieu
>
> * 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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