mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-30 12:10:37 +00:00
105 lines
3.8 KiB
Text
105 lines
3.8 KiB
Text
Tracing
|
|
=======
|
|
|
|
This subsystem will provide a mechanism to get structured tracing info from GStreamer
|
|
applications. This can be used for post-run analysis as well as for live
|
|
introspection.
|
|
|
|
We are going to introduce a GstTracer object. There will be only a single instance
|
|
per process or none if tracing is off (not enabled via envvar or compiled out).
|
|
|
|
Certain GStreamer core function (such as gst_pad_push or gst_element_add_pad) will
|
|
call into the tracer. The tracer will dispatch into loaded tracing plugins.
|
|
Developers will be able to select a list of plugins by setting an environment
|
|
variable, such as GST_TRACE="meminfo,dbus". When then plugins are loaded, they will
|
|
add them to certain hooks. Another env var GST_TRACE_CHANNEL can be used to send
|
|
the tracing to a file or a socket (Do the same for GST_DEBUG_CHANNEL). The syntax
|
|
could be GST_XXX_CHANNEL=file:///path/to/file or GST_XXX_CHANNEL=tcp://<ip>:<port>.
|
|
If no channel is set, the tracing goes to stderr like the debug logging.
|
|
|
|
TODO(ensonic): we might want to have GST_{DEBUG|TRACE)_FORMAT envars as well. These
|
|
could be raw, ansi-color, binary, ...
|
|
|
|
Hooks
|
|
-----
|
|
e.g. gst_pad_push() will do add this line:
|
|
GST_TRACER_PUSH_BUFFER (pad, buffer)
|
|
|
|
If tracing is disable at compile time the macro will evaluate to nothing. Otherwise
|
|
it will become something along the lines of:
|
|
if (__tracer && __tracer_hook_is_used) {
|
|
gst_tracer_push_buffer (pad, buffer);
|
|
}
|
|
|
|
TODO(ensonic): we should eval if we can use something like jump_label in the kernel
|
|
- http://lwn.net/Articles/412072/ + http://lwn.net/Articles/435215/
|
|
- http://lxr.free-electrons.com/source/kernel/jump_label.c
|
|
- http://lxr.free-electrons.com/source/include/linux/jump_label.h
|
|
- http://lxr.free-electrons.com/source/arch/x86/kernel/jump_label.c
|
|
TODO(ensonic): liblttng-ust provides such a mechanism for user-space
|
|
- but this is mostly about logging traces
|
|
- it is linux specific :/
|
|
|
|
In addition to api hooks we should also provide timer hooks. Interval timers are
|
|
useful to get e.g. resource usage snapshots. Also absolute timers might make sense.
|
|
|
|
Plugins can attach handlers to one or more hooks. When a hook such as
|
|
gst_tracer_push_buffer () is called it will take a timestamp and call all attached
|
|
handlers. Hooks will be called from misc threads. The trace plugins should only
|
|
consume (=read) the provided data. Most trace plugins will log data to a trace
|
|
channel.
|
|
|
|
TODO(ensonic): use GSignal for the hooks?
|
|
|
|
Plugins
|
|
=======
|
|
|
|
meminfo
|
|
-------
|
|
- register to an interval-timer hook.
|
|
- call mallinfo() and log memory usage
|
|
|
|
rusage
|
|
------
|
|
- register to an interval-timer hook.
|
|
- call getrusage() and log resource usage
|
|
|
|
dbus
|
|
----
|
|
- provide a dbus iface to announce applications that are traced
|
|
- tracing UIs can use the dbus iface to find the channels where logging and tracing
|
|
is getting logged to, one would start the tracing UI first and when the
|
|
application is started with tracing activated, the dbus plugin will announce the
|
|
new application, upon which the tracing UI can start reading from the log channels
|
|
|
|
topology
|
|
--------
|
|
- register to pipeline topology hooks
|
|
- tracing UIs can show a live pipeline graph
|
|
|
|
communication
|
|
-------------
|
|
- register to buffer, event, message and query flow
|
|
- tracing apps can do e.g. statistics
|
|
|
|
UI
|
|
==
|
|
|
|
gst-debug-viewer
|
|
----------------
|
|
gst-debug-viewer could be given the tracelog in addition to the debug log.
|
|
Alternatively it would show a dialog that shows all local apps (if the dbus plugin
|
|
is loaded) and read the log streams from the sockets/files that are configured for
|
|
the app.
|
|
|
|
gst-trace-stats
|
|
---------------
|
|
Such a tool could read a trace and summarize the content like gst-tracelib did for
|
|
stats in 0.10.
|
|
|
|
|
|
Problems / Open items
|
|
=====================
|
|
- when connecting to a running app, we cant easily get the 'current' state if logging
|
|
is using a socket, as past events are not stored
|
|
|