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design: tracing: section breakdown, markup and readability fixes

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Reynaldo H. Verdejo Pinochet 2016-12-30 01:12:41 -08:00
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markdown/design/tracing.md
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@ -4,7 +4,7 @@ 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.
# Use cases
## Use cases
- I’d like to get statistics from a running application.
@ -16,12 +16,12 @@ well as for live introspection.
- I’d like to know about ref-counts of parts in the pipeline to find
ref-count issues.
# Non use-cases
## Non use-cases
- Some element in the pipeline does not play along the rules, find out
which one. This could be done with generic tests.
# Design
## Design
The system brings the following new items: core hooks: probes in the
core api, that will expose internal state when tracing is in use
@ -31,29 +31,29 @@ log tracing front-ends: applications that consume logs from tracers
Like the logging, the tracer hooks can be compiled out and if not use a
local condition to check if active.
Certain GStreamer core function (such as gst_pad_push or
gst_element_add_pad) will call into the tracer subsystem to dispatch
Certain GStreamer core function (such as `gst_pad_push()` or
`gst_element_add_pad()`) will call into the tracer subsystem to dispatch
into active tracing modules. Developers will be able to select a list of
plugins by setting an environment variable, such as
GST_TRACERS="meminfo;dbus". One can also pass parameters to plugins:
GST_TRACERS="log(events,buffers);stats(all)". When then plugins are
`GST_TRACERS="meminfo;dbus"`. One can also pass parameters to plugins:
`GST_TRACERS="log(events,buffers);stats(all)"`. When then plugins are
loaded, we’ll add them to certain hooks according to which they are
interested in.
Right now tracing info is logged as GstStructures to the TRACE level.
Idea: Another env var GST_TRACE_CHANNEL could be used to send the
Right now tracing info is logged as `GstStructures` to the TRACE level.
Idea: Another env var `GST_TRACE_CHANNEL` could be used to send the
tracing to a file or a socket. See
<https://bugzilla.gnome.org/show_bug.cgi?id=733188> for discussion on
these environment variables.
# Hook api
## Hook api
We’ll wrap interesting api calls with two macros, e.g. gst_pad_push():
GstFlowReturn gst_pad_push (GstPad * pad, GstBuffer * buffer) {
GstFlowReturn res;
We’ll wrap interesting api calls with two macros, e.g. `gst_pad_push()`:
``` c
GstFlowReturn gst_pad_push (GstPad * pad, GstBuffer * buffer) {
GstFlowReturn res;
g_return_val_if_fail (GST_IS_PAD (pad), GST_FLOW_ERROR);
g_return_val_if_fail (GST_PAD_IS_SRC (pad), GST_FLOW_ERROR);
g_return_val_if_fail (GST_IS_BUFFER (buffer), GST_FLOW_ERROR);
@ -82,13 +82,14 @@ 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. All this could be implemented with a clock
thread. We can use another env-var GST_TRACE_TIMERS="100ms,75ms" to
thread. We can use another env-var `GST_TRACE_TIMERS="100ms,75ms"` to
configure timers and then pass them to the tracers like,
GST_TRACERS="rusage(timer=100ms);meminfo(timer=75ms)". Maybe we can
create them ad-hoc and avoid the GST_TRACE_TIMERS var.
`GST_TRACERS="rusage(timer=100ms);meminfo(timer=75ms)"`. Maybe we can
create them ad-hoc and avoid the `GST_TRACE_TIMERS` var.
Hooks (* already implemented)
Hooks (\* already implemented)
```
* gst_bin_add
* gst_bin_remove
* gst_element_add_pad
@ -102,6 +103,7 @@ Hooks (* already implemented)
* gst_pad_push_list
* gst_pad_push_event
* gst_pad_unlink
```
## Tracer api
@ -110,7 +112,7 @@ Tracers are plugin features. They have a simple api:
class init Here the tracers describe the data the will emit.
instance init Tracers attach handlers to one or more hooks using
gst_tracing_register_hook(). In case the are configurable, they can
`gst_tracing_register_hook()`. In case the are configurable, they can
read the options from the *params* property. This is the extra detail
from the environment var.
@ -122,8 +124,8 @@ the execution too much. Most trace plugins will log data to a trace
channel.
instance destruction Tracers can output results and release data. This
would ideally be done at the end of the applications, but gst_deinit()
is not mandatory. gst_tracelib was using a gcc_destructor. Ideally
would ideally be done at the end of the applications, but `gst_deinit()`
is not mandatory. `gst_tracelib` was using a `gcc_destructor`. Ideally
tracer modules log data as they have them and leave aggregation to a
tool that processes the log.
@ -138,7 +140,7 @@ One way would be to introspect the data from the plugin. This has the
disadvantage that the postprocessing app needs to load the plugins or
talk to the gstreamer registry. An alternative is to also log the format
description into the log. Right now we’re logging several nested
GstStructure from the `tracer_class_init()` function (except in the
`GstStructure` from the `tracer_class_init()` function (except in the
log tracer).
```
@ -187,8 +189,8 @@ qdata for scope and flags (or have some new property flags). We would also
need a new "notify" signal, so that value-change notifications would include a
time-stamp. This way the tracers would not needs to be aware of the
logging. The core tracer would register the notify handlers and emit the
log. Or we just add a gst_tracer_class_install_event() and that
mimics the g_object_class_install_property().
log. Or we just add a `gst_tracer_class_install_event()` and that
mimics the `g_object_class_install_property()`.
Frontends can:
- do an events over time histogram
@ -205,9 +207,9 @@ Frontends can:
## meminfo (not yet implemented)
- register to an interval-timer hook.
- call mallinfo() and log memory usage rusage
- call `mallinfo()` and log memory usage rusage
- register to an interval-timer hook.
- call getrusage() and log resource usage
- call `getrusage()` and log resource usage
## dbus (not yet implemented)
@ -249,14 +251,14 @@ extensions)
## leaks
- track creation/destruction of GstObject and GstMiniObject
- track creation/destruction of `GstObject` and `GstMiniObject`
- log those which are still alive when app is exiting and raise an
error if any
- The tracer takes several parameters in a GstStructure like syntax (without the structure name):
- The tracer takes several parameters in a `GstStructure` like syntax (without the structure name):
- check-refs (boolean): Whether to also track object ref and unref operations
example: GST_TRACERS=leaks(check-refs=true) COMMAND
example: `GST_TRACERS=leaks(check-refs=true)` COMMAND
- stack-traces-flags: Flags to use when generating stack trace (does not generate stack trace
if not set), valid values are “full” to retrieve as much information as possible in the
backtrace, or “none” for a simple backtrace (usually does not contain line number or source files).
@ -265,7 +267,7 @@ extensions)
- filters: (string): A comma separated list of object types to trace (make sure to enclose in
quotation marks)
**Run the leaks tracer on all GstProxyPad objects logging the references with a full backtraces**
**Run the leaks tracer on all `GstProxyPad` objects logging the references with a full backtraces**
```
GST_TRACERS=leaks(stack-traces-flags=full,filters=”GstProxyPad”,check-refs=true) COMMAND
@ -277,7 +279,7 @@ GST_TRACERS=leaks(stack-traces-flags=full,filters=”GstProxyPad”,check-refs=t
GST_TRACERS=leaks(stack-traces-flags=fast,check-refs=true) COMMAND
```
- If the GST_LEAKS_TRACER_SIG env variable is defined the tracer
- If the `GST_LEAKS_TRACER_SIG` env variable is defined the tracer
will handle the following UNIX signals:
- SIGUSR1: log alive objects
@ -315,21 +317,21 @@ little driver * <https://github.com/dkogan/feedgnuplot>
- worse performance (we’re writing two logs at the same time)
- need to be careful when people to GST_DEBUG_CHANNEL=stderr and
- need to be careful when people to `GST_DEBUG_CHANNEL=stderr` and
GST_TRACE_CHANNEL=stderr (use a shared channel, but what about the
formats?)
- debug log
- the tracer subsystem would need to log the GST_TRACE at a level
- the tracer subsystem would need to log the `GST_TRACE` at a level
that is active
- should the tracer call gst_debug_category_set_threshold() to
- should the tracer call `gst_debug_category_set_threshold()` to
ensure things work, even though the levels don’t make a lot of sense
here
- make logging a tracer (a hook in gst_debug_log_valist, move
gst_debug_log_default() to the tracer module)
- make logging a tracer (a hook in `gst_debug_log_valist()`, move
`gst_debug_log_default()` to the tracer module)
- log all debug log to the tracer log, some of the current logging
statements can be replaced by generic logging as shown in the
@ -346,72 +348,86 @@ little driver * <https://github.com/dkogan/feedgnuplot>
intervals?
- can we add a tracer module that registers the timer hook? then we
could do GST_TRACER="timer(10ms);rusage" right now the tracer hooks
could do `GST_TRACER="timer(10ms);rusage"` right now the tracer hooks
are defined as an enum though.
- when connecting to a running app, we can’t easily get the *current*
state if logging is using a socket, as past events are not
explicitly stored, we could determine the current topology and emit
events with GST_CLOCK_TIME_NONE as ts to indicate that the events
events with `GST_CLOCK_TIME_NONE` as ts to indicate that the events
are synthetic.
- we need stable ids for scopes (threads, elements, pads)
- the address can be reused
- we can use gst_util_seqnum_next()
- we can use `gst_util_seqnum_next()`
- something like gst_object_get_path_string() won’t work as
- something like `gst_object_get_path_string()` won’t work as
objects are initially without parent
- right now the tracing-hooks are enabled/disabled from configure with
--{enable,disable}-gst-tracer-hooks The tracer code and the plugins
`--{enable,disable}-gst-tracer-hooks` The tracer code and the plugins
are still built though. We should add a
--{enable,disable}-gst-tracer to disabled the whole system,
allthough this is a bit confusing with the --{enable,disable}-trace
`--{enable,disable}-gst-tracer` to disabled the whole system,
allthough this is a bit confusing with the `--{enable,disable}-trace`
option we have already.
## Try it
### Traces for buffer flow, events and messages in TRACE level:
GST_DEBUG="GST_TRACER:7,GST_BUFFER*:7,GST_EVENT:7,GST_MESSAGE:7"
GST_TRACERS=log gst-launch-1.0 fakesrc num-buffers=10 ! fakesink -
```
GST_DEBUG="GST_TRACER:7,GST_BUFFER*:7,GST_EVENT:7,GST_MESSAGE:7"
GST_TRACERS=log gst-launch-1.0 fakesrc num-buffers=10 ! fakesink -
```
### Print some pipeline stats on exit:
GST_DEBUG="GST_TRACER:7" GST_TRACERS="stats;rusage"
GST_DEBUG_FILE=trace.log gst-launch-1.0 fakesrc num-buffers=10
sizetype=fixed ! queue ! fakesink && gst-stats-1.0 trace.log
```
GST_DEBUG="GST_TRACER:7" GST_TRACERS="stats;rusage"
GST_DEBUG_FILE=trace.log gst-launch-1.0 fakesrc num-buffers=10
sizetype=fixed ! queue ! fakesink && gst-stats-1.0 trace.log
```
### get ts, average-cpuload, current-cpuload, time and plot
GST_DEBUG="GST_TRACER:7" GST_TRACERS="stats;rusage"
GST_DEBUG_FILE=trace.log /usr/bin/gst-play-1.0 $HOME/Videos/movie.mp4 &&
./scripts/gst-plot-traces.sh --format=png | gnuplot eog trace.log.*.png
```
GST_DEBUG="GST_TRACER:7" GST_TRACERS="stats;rusage"
GST_DEBUG_FILE=trace.log /usr/bin/gst-play-1.0 $HOME/Videos/movie.mp4 &&
./scripts/gst-plot-traces.sh --format=png | gnuplot eog trace.log.*.png
```
### print processing latencies
GST_DEBUG="GST_TRACER:7" GST_TRACERS=latency gst-launch-1.0 \
audiotestsrc num-buffers=10 ! audioconvert ! volume volume=0.7 ! \
autoaudiosink
```
GST_DEBUG="GST_TRACER:7" GST_TRACERS=latency gst-launch-1.0 \
audiotestsrc num-buffers=10 ! audioconvert ! volume volume=0.7 ! \
autoaudiosink
```
### Raise a warning if a leak is detected
GST_TRACERS="leaks" gst-launch-1.0 videotestsrc num-buffers=10 !
fakesink
```
GST_TRACERS="leaks" gst-launch-1.0 videotestsrc num-buffers=10 !
fakesink
```
### check if any GstEvent or GstMessage is leaked and raise a warning
GST_DEBUG="GST_TRACER:7" GST_TRACERS="leaks(GstEvent,GstMessage)"
gst-launch-1.0 videotestsrc num-buffers=10 ! fakesink
```
GST_DEBUG="GST_TRACER:7" GST_TRACERS="leaks(GstEvent,GstMessage)"
gst-launch-1.0 videotestsrc num-buffers=10 ! fakesink
```
# Performance
## Performance
run ./tests/benchmarks/tracing.sh <tracer(s)> <media>
```
run ./tests/benchmarks/tracing.sh <tracer(s)> <media>
egrep -c "(proc|thread)-rusage" trace.log 658618 grep -c
"gst_tracer_log_trace" trace.log 823351
egrep -c "(proc|thread)-rusage" trace.log 658618 grep -c
"gst_tracer_log_trace" trace.log 823351
```
- we can optimize most of it by using quarks in structures or
eventually avoid structures totally