[ltt-dev] some question about ltt

Mathieu Desnoyers compudj at krystal.dyndns.org
Mon Jan 31 11:02:24 EST 2011


* loody (miloody at gmail.com) wrote:
> hi all:
> I have some questions about ltt:
> 1. what is the out format about ltt?
> it seems kernel.softirq_entry mean it calls softirq_entry and belongs
> to kernel group


> but what does metadata.core_marker_format mean?

group metadata (lttng trace metadta), which outputs the id/format of
events. It describes the rest of the trace.

> Calling core_marker_format? and what does metadata group mean?
> 2. ltt is used for monitoring kernel behavior, why there is a group
> named "userspace"?

It contains the events written through the debugfs file ltt/write_event.
See "Userspace tracing" in the LTTng Manual on the lttng.org website.
This is a "slow" tracing mode that takes a simple string as input. UST
is a much faster tracer that hooks directly onto tracepoints declared in
userspace code.

> 3. can I monitor the system calls, "set_thread_area" and "mprotect"?

Yes. But you will see them as "syscall_entry/syscall_exit" events, with
the syscall number mapping to the syscall name (first event field). We
don't gather the syscall arguments at this point: you'll need to add
instrumentation for that.



> I found these 2 functions in strace but cannot found it in ltt.
> Should I open additional config ?

Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.

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