Re: Help adding trace events to xHCI

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

* Mark Wielaard (mjw@redhat.com) wrote:
> Hi Mathieu,
> 
> On Fri, Jul 12, 2013 at 01:08:28PM -0400, Mathieu Desnoyers wrote:
> > * Sarah Sharp (sarah.a.sharp@linux.intel.com) wrote:
> > > Thanks for the suggestion.  I'm not familiar with all the userspace
> > > tools for trace events, so I didn't know about the command parser.  Is
> > > there documentation or a list of resources for all the userspace trace
> > > event plugins?  If so, can you give us a pointer to it?
> > 
> > You might want to try out LTTng-UST. It provides TRACEPOINT_EVENT() and
> > tracepoint() for user-space instrumentation. See:
> > 
> > - https://lttng.org/files/doc/man-pages/man3/lttng-ust.3.html
> 
> Is that build on the <sys/sdt.h> ust probe points as embedded in glibc
> for example that gdb and systemtap use to access user space trace
> points?

LTTng-UST tracepoints are not built on sdt.h, but they can optionally
emit sdt.h instrumentation. All you need to do is run:

./configure --with-sdt

when configuring lttng-ust, and after a make install, sdt.h
STAP_PROBEV() will be emitted whenever a lttng-ust tracepoint() macro is
used in the system.

> Can tools use lttng-ust and <sys/sdt.h> tracepoints
> interchangeably by parsing the ELF notes described in
> http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation

Since lttng-ust tracepoints emit sdt.h instrumentation, yes. However,
please note that the reverse is not possible: sdt.h instrumentation does
not allow tracing with LTTng-UST.

Thanks,

Mathieu

> 
> Thanks,
> 
> Mark

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com