[Qemu-devel] [PATCH 0/2] trace: fix trace_event_get_state() for SystemTap and LTTng UST

[Stefan Hajnoczi]

Trace events that compute their arguments can affect performance.  The
following idom can be used to avoid computing arguments when the trace event is
disabled:

  if (trace_event_get_state(TRACE_MY_EVENT)) {
      char *str = g_strdup_printf("Expensive string ...", ...);
      trace_my_event(str);
      g_free(str);
  }

Unfortunately this breaks the trace event for SystemTap and LTTng UST since
those tracers manage their own enabled/disabled state.

These patches add per-backend dstate to trace_event_get_state() so that the
trace event fires as expected when enabled via SystemTap or LTTng UST.

Stefan Hajnoczi (2):
  trace: add TRACE_<event>_BACKEND_DSTATE()
  trace: check backend dstate in trace_event_get_state()

 trace/control.h                       | 20 ++++++++++++++++++--
 scripts/tracetool/__init__.py         |  1 +
 scripts/tracetool/backend/__init__.py |  3 +++
 scripts/tracetool/backend/dtrace.py   | 12 ++++++++++++
 scripts/tracetool/backend/ftrace.py   |  2 +-
 scripts/tracetool/backend/log.py      |  3 ++-
 scripts/tracetool/backend/simple.py   |  2 +-
 scripts/tracetool/backend/syslog.py   |  3 ++-
 scripts/tracetool/backend/ust.py      |  5 +++++
 scripts/tracetool/format/h.py         | 10 ++++++++++
 10 files changed, 55 insertions(+), 6 deletions(-)

-- 
2.13.3