[ltt-dev] LTTng and Timestamps mismatch

[Brosseau, Yannick]

I've have some patch to make LTTng 2.0 works on a 2.6.32 kernel. I'll
post that soon...

On Wed, Nov 23, 2011 at 12:53 PM, Abhishek Karoliya <abhikaro at gmail.com> wrote:
> Thanks Mathieu for the pointers...
>
> I have got a half cooked third party kernel when it comes to lttng
> patches which is making it harder than it has to get to the code. The
> kernel has been applied with Lttng patches but no one knows which
> version of the patch reside. Off target but it will be immense help is
> you or anyone could give help me deduce what kernel patch version has
> been applied. What files or strings I could search? It is a 2.6.34
> kernel with pre-empt rt patch.
>
> I am all for 2.0 but the program here hasn't progressed to 2.6.35 and
> it will be some time before we will start using it.
>
> On Tue, Nov 22, 2011 at 11:50 AM, Mathieu Desnoyers
> <compudj at krystal.dyndns.org> wrote:
>> * Abhishek Karoliya (abhikaro at gmail.com) wrote:
>>> Hello People,
>>>
>>> I am using LTTng to get around a scheduling and priority inheritance
>>> problem that we are observing on our system (powerpc e500v2 dual core,
>>> linux 2.6.34). However, I need map timestamps for events as seen in
>>> Lttng trace, kernel and application (I am using TSC divided by time
>>> base freq for application). I see that even though stop tracing
>>> (lttctl -D ) at 601.xxxxxx (/var/log/kernel )
>>> Nov 21 16:26:13 XRX9C93E4059FFD kernel: [  601.695548] LTT: 284 events
>>> written in channel metadata (cpu 1, index 0)
>>> Nov 21 16:26:13 XRX9C93E4059FFD kernel: [  601.710868] LTT: 40 events
>>> written in channel module_state (cpu 1, index 0)
>>> ...............................................
>>> Nov 21 16:26:13 XRX9C93E4059FFD kernel: [  601.710978] LTT: 32 events
>>> written in channel softirq_state (cpu 1, index 0)
>>>
>>> When I look dump the trace using lttv, I can see events that are
>>> timestamped upto 670.xxxxxxxx.
>>>
>>> I am wondering if this is due some timing offset? If yes, how could I
>>> match them?
>>>
>>> My Setup
>>> ltt-control-0.89-05122011
>>> lttv-0.12.36-18112010
>>> linux-2.6.32 with pre-empt RT patch
>>>
>>> Any pointers will be greatly appreciated.
>>
>> The LTTng timestamps, on powerpc, are directly derived from the TB
>> register value, without offset. The timestamp used in printk logs is
>> based, if my memory serves me correctly, on the kernel monotonic clock.
>> You might want to check what offset they apply to this clock, or try to
>> record the data from userspace through the marker_event (was theat even
>> the exact name, not sure anymore) debugfs file exposed by lttng through
>> debugfs. It's also possible that the printk timestamps are based on the
>> current time of day, which is offset by the ntp-correction.
>>
>> Or you can try lttng 2.0. It comes with kernel and user-level tracing.
>> For the moment, it uses the CLOCK_MONOTONIC clock source both both
>> kernel and user-level tracing (until we reimplement the trace clocks
>> into lttng 2.0 and the vDSOs for userspace LTTng-UST). We also have the
>> dynamic task priority and nice level that we can record along with
>> events (see lttng add-context), which will be tremendously useful to
>> debug the kind of priority inversion problem you are investigating.
>>
>> However, you need a kernel version >= 2.6.35 to build the lttng-modules.
>> No kernel patches are required (it's just a module package).
>>
>> For more info, see http://lttng.org/lttng2.0
>>
>> Best regards,
>>
>> Mathieu
>>
>>
>>>
>>> Thanks
>>> Abhi
>>>
>>> _______________________________________________
>>> ltt-dev mailing list
>>> ltt-dev at lists.casi.polymtl.ca
>>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>>
>>
>> --
>> Mathieu Desnoyers
>> Operating System Efficiency R&D Consultant
>> EfficiOS Inc.
>> http://www.efficios.com
>>
>
> _______________________________________________
> ltt-dev mailing list
> ltt-dev at lists.casi.polymtl.ca
> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>



-- 
Yannick Brosseau
www.projetmontreal.org
Consultant en logiciel libre
yannickbrosseau.com