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

[compudj@krystal.dyndns.org (Mathieu Desnoyers)]

* 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,

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