[ltt-dev] Problem on combine kernel trace and userspace trace.

[Sam Liao]

On Wed, Nov 3, 2010 at 11:13 PM, Mathieu Desnoyers
<compudj at krystal.dyndns.org> wrote:
> * Sam Liao (phyomh at gmail.com) wrote:
>> Hi,
>>
>> I'm trying to combine the kernel trace and userspace trace, and it
>> seems that the
>> the userspace events can not be recognized to the right process with the kernel
>> events. I'm not sure if this is a problem of timestamp between kernel
>> and userspace.
>>
>> Here is the environment I'm using:
>> ----
>> Linux Trace Toolkit Visualizer 0.12.35-20082010
>> linux kernel 2.6.34.6
>> ust-0.4. ( I update the clock to use clock_gettime).
>
> If you are on x86 or powerpc, using the clock source that does not use
> clock_gettime would directly read the timestamp counter value, which
> should work. Make sure your architecture (on x86) has synchronized
> contant TSCs. LTTng complains about using a work-around in dmesg if it
> is not the case. If lttng uses the workaround on x86, then there is
> currently no mean to gather synchronized ust-lttng traces. As Julien
> said, we're currently working on a vdso solution to make this all work.
>

Thanks, after apply with the "rdtsc" clock source and set up the correct
clock frequency,  the kernel trace and ust trace seems to be consistent
now.

Thanks,
-Sam

> Thanks,
>
> Mathieu
>
>> ----
>>
>> Is there anything I missed? Also I'm thinking about one problem, if
>> ust using clock_gettime to
>> get the nonseconds timestamp which is actually the timestamp that the user
>> application is doing the clock_gettime system call instead the
>> userspace event, how ust
>> deal with such difference and get this fixed when trace combination?
>>
>> Thanks,
>> -Sam
>>
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>>
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>