Skip to main content
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [List Home]
Re: [tracecompass-dev] Synchronizing LTTng Kernel and UST Traces ?
That is weird, because both UST and kernel traces uses the same time source (clock_gettime(CLOCK_MONOTONIC_RAW)), so they don't need synchronization. 

I did a trace with kernel and ust, the app is called wk-heartbeat and generate one event each seconds. The heartbeat event occurs in the right context and is perfectly aligned with the kernel trace without any synchronization.

pasted1

You can try to reproduce this view with the following trace: 

Francis

Le jeu. 17 déc. 2015 à 03:52, Oberhuber, Martin <Martin.Oberhuber@xxxxxxxxxxxxx> a écrit :

Hi Tracecompass Experts,

 

I have obtained an LTTng-UST and Kernel Trace in parallel, but looking at the respective combined experiment it turns out that Kernel and UST seem to use different time sources (there’s a time skew).  Consider attached screenshot: The UST event is shown in the middle of syscall state, but it would be expected in “lemon_server RUNNING” state.

 

Reading the Trace Compass docs, I see that there’s a synchronization feature, but only for network traces and only with experimental branches enabled.

 

What could be done to get Kernel and UST traces synchronized ? Or should a completely different method of data gathering be considered, eg doing “perf record” with uprobes enabled and then converting the perf.data to CTF for investigation ? Correlating application traces with Kernel event seems a powerful tool to me for understanding excessive latencies … perhaps adding UST pthread events could help with trace synchronization since these should exist on Kernel and UST side ?

 

Many thanks for any pointers !!

 

PS my sample trace was obtained on Linux qemux86, Kernel 4.1 with lttng-2.6. I’m happy to share the recorded traces if anybody is interested.

 

Thanks,

Martin

--

Martin Oberhuber, SMTS / Product Owner – Development Tools, Wind River

direct +43.662.457915.85  fax +43.662.457915.6

 

_______________________________________________
tracecompass-dev mailing list
tracecompass-dev@xxxxxxxxxxx
To change your delivery options, retrieve your password, or unsubscribe from this list, visit
https://dev.eclipse.org/mailman/listinfo/tracecompass-dev

Back to the top