[ltt-dev] Babeltrace timestamp problem

[Mathieu Desnoyers]

Thanks for the clear and repeatable bug report! It should be fixed in
commit 5f643ed7d0d2d21d3797938e34735ef8f1bd9186

Mathieu

* Simon Marchi (simon.marchi at polymtl.ca) wrote:
> Hello,
> 
> I think there may be a little problem with the accuracy of the
> timestamps read by babeltrace.
> 
> Here is what I did:
> 
> (code available here, if you want it
> http://git.dorsal.polymtl.ca/~smarchi?p=babeltrace.git;a=shortlog;h=refs/heads/timestampdebug)
> 
> 1- Hijack the ctf_update_timestamp function in ctf.c so that we log in
> a file all the timestamp that are read from the CTF format.
> 
> 2- Have the dummy output format output log the timestamp of all
> "written" events in an other file.
> 
> 3- Sort the output of #1 (with coreutils sort), because at this point
> they do not come out sorted.
> 
> 4- Compare both. They should be identical, but they are not.
> 
> I compared a similarly formatted output of the Java parser, and it is
> identical to the file of #1.
> 
> I noticed that the differences often look like this:
> 
> @@ -368,10 +368,10 @@
>  248813704165405
>  248813704165482
>  248813704166130
> -248813704166315
>  248813704169065
>  248813704169935
>  248813704170150
> +248813704170150
>  248813704171110
>  248813704171937
>  248813704176084
> @@ -400,7 +400,7 @@
>  248813704252089
>  248813704252267
>  248813704253474
> -248813704254629
> +248813704255344
>  248813704255344
>  248813704255859
>  248813704256404
> 
> where a good timestamp (the minus in the diff) is overwritten by a
> later timestamp (the plus in the diff). Sometimes, like in the first
> example, they (the timestamp that gets overwritten and the timestamp
> that overwrites) are not contiguous at the trace level, but every time
> I checked, they were next to each other at the stream (file) level. So
> that means the problem is probably somewhere in the handling of
> ctf_stream.timestamp.
> 
> Simon
> 
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> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com