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

[julien.desfossez@polymtl.ca (Julien Desfossez)]

Hi Sam,

Thanks for posting this, regarding the issue with time synchronization
of the traces, we are actually working exactly on it right now.
The main problem for now is that the events are recorded in cycles in
the trace which means we need to know the TSC frequency to convert back
in sec.nsec in LTTV. From UST we don't have a clear way to access this
information, so we are now working on a new option in clock_gettime to
use the LTTng trace clock infrastructure to make it easy to synchronise
kernel and ust traces. I will post more details soon.

Regarding the possibility of combining the userspace and kernelspace
events for the same process I'm not sure exactly how it works, from what
I can see the PID is 0 in UST traces so the traces cannot really be
merged but I will let the people more familiar with UST answer this one.

Thanks,

Julien


On 10-11-03 05:24 AM, Sam Liao 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).
> ----
> 
> 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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