[lttng-dev] faulty context for sched_stat_ tracepoints?

[Luetkebohle Ingo (CR/AEA2)]

Hi,

I noticed that the "procname" and "tid" *context* variables can differ from the "comm" and "tid" variables of the sched_stat_-tracepoints (e.g., for sched_stat_runtime).

For example, see the following two outputs:
[15:49:33.674072890] (+0.000029771) rng2070 sched_stat_sleep: { cpu_id = 4 }, { pid = 26974, procname = "amcl", tid = 26975 }, { comm = "lttng-sessiond", tid = 798, delay = 194122524 }
[15:49:33.722894563] (+0.000004851) rng2070 sched_stat_sleep: { cpu_id = 0 }, { pid = 0, procname = "swapper/0", tid = 0 }, { comm = "amcl", tid = 27078, delay = 10043658 }

In both cases, procname differs from comm.  I've looked at the kernel source code, and the "comm" variable is taken from task_struct.filename. Barring renames, this would be the correct one, so I'm assuming that the context is sometimes incorrect.

Now, for this particular case, I can take the correct variables from the tracepoint, but of course, this makes me worried that the context might also be wrong in other cases... Do you have any idea what could be going on here?

LTTng is Version 2.7.x+stable+bzr2948+pack17+201511192116~ubuntu14.04.1 and this is on a 3.19.0-33-generic kernel (btw, that's not the default kernel for Ubuntu 14.04, but the LTS vivid backport kernel).

Mit freundlichen Grüßen / Best regards

Ingo Luetkebohle

Application Software (CR/AEA2)
Tel. +49(711)811-12248 | Fax +49(711)811-0 | Ingo.Luetkebohle at de.bosch.com<mailto:Ingo.Luetkebohle at de.bosch.com>


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