[lttng-dev] combined kernel and userspace trace

[Jonathan Rajotte-Julien]

Hi,

On Thu, Jun 01, 2017 at 12:49:50PM +0000, Deneau, Tom wrote:
> Using, lttng 2.9.4
> 
> Doing combined kernel and usermode tracing and then looking at the combined trace with babeltrace...
> I have noticed there is often a period at the beginning of the combined trace which is all kernel events and similarly a period at the end of the combined trace which is all userspace events.
> 
> I suppose I can just search for the section in the middle where both channels are active but is there any way to eliminate the single-channel sections at the beginning and end?

There is no automatic way to do this as of today. A manual alternative would be
to seek to the point of interest and make babeltrace start/end there.

Unfortunately, babeltrace 1.5 does not support seeking to a position via the command line.
The long awaited Babeltrace 2 should allow easy seeking to your point of interest.

> 
> Also, is it guaranteed that once I get to the section where both channels appear active in the trace that I will be seeing all events in the combined trace?

Not sure what you mean here. As long as you do not have discarded events at
production Babeltrace will show all events from both traces(ust &
kernel) in orders based on clock.

Cheers

> 
> -- Tom Deneau
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-- 
Jonathan Rajotte-Julien
EfficiOS