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ROS time (sim_time) support#

Introduction#

CARET uses system time to analyze trace data by default. It may be inconvenient, especially when treating trace data recorded with rosbag. These are examples:

  • The flow of time in analysis results (e.g., time series graph) is different from that of ROS when playing rosbag with [-r RATE] option. For instance, 10 Hz becomes 2 Hz when rosbag was played with [-r 0.2] but analysis uses system time
  • Time becomes different at every recording even if you use the same rosbag file, which makes comparing experimental results difficult

This page explains how to use sim_time.

Recording /clock topic#

/clock topic needs to be recorded in trace data. /clock topis is recorded as ros2_caret:sim_time event in trace data.

Add the --record-clock option to the ros2 caret record command.

Info

Remember to set use_sim_time=true for each node when launching a target application Remember to add --clock option when playing rosbag

source /opt/ros/humble/setup.bash
source ~/ros2_caret_ws/install/local_setup.bash

ros2 caret record --record-clock

You can check whether /clock is successfully recorded by the following command.

babeltrace <path-to-trace-data> | cut -d' ' -f 4 | sort -u | grep sim_time

---Expected output text as below---

ros2_caret:sim_time:

Visualization using sim_time#

By setting xaxis_type='sim_time', sim_time is used instead of system time for the following APIs in Plot object.

def to_dataframe(
   self,
   xaxis_type: str
) -> pd.DataFrame:

def figure(
   self,
   xaxis_type: Optional[str],
   ywheel_zoom: Optional[bool],
   full_legends: Optional[bool]
) -> Figure:

def show(
    self,
    xaxis_type: str = 'system_time',
    ywheel_zoom: bool = True,
    full_legends: bool = False,
) -> None:

def save(
    self,
    export_path: str,
    title: str = '',
    xaxis_type: Optional[str] = None,
    ywheel_zoom: Optional[bool] = None,
    full_legends: Optional[bool] = None
) -> None:

In case /clock topic is not recorded in trace data, the following error will occur.

InvalidArgumentError: Failed to load sim_time. Please measure again with clock_recorder running.

Warning

If the timer callback exists in middle of the target path, ROSBAG playback rate significantly affects the behavior of the path. As a result, even when xaxis_type is 'sim_time', response time of the path cannot be calculated correctly for the trace data whose ROSBAG playback rate is not 1.0.

Sample to use sim_time#

Explanation below assumes CARET is installed to ~/ros2_caret_ws and the sample application used in the tutorial section is located in ~/ros2_ws.

Record rosbag#

The following steps can be performed either with or without CARET. If you have built a target application without CARET, you don't need to set environment for CARET and LD_PRELOAD.

  1. Open a terminal to run a target application to record rosbag

    source /opt/ros/humble/setup.bash
source ~/ros2_caret_ws/install/local_setup.bash
source ~/ros2_ws/install/local_setup.bash
export LD_PRELOAD=$(readlink -f ~/ros2_caret_ws/install/caret_trace/lib/libcaret.so)

ros2 run caret_demos end_to_end_sample

  2. Open another terminal to record rosbag

    source /opt/ros/humble/setup.bash
source ~/ros2_caret_ws/install/local_setup.bash
source ~/ros2_ws/install/local_setup.bash

ros2 bag record /topic1 /drive

    Here, /topic1 and /drive are source topics of the sample application. You can check if rosbag is successfully recorded.

    ros2 bag info rosbag2_2022_09_30-10_57_06

Files:             rosbag2_2022_09_30-10_57_06_0.db3
Bag size:          29.3 KiB
Storage id:        sqlite3
Duration:          9.601s
Start:             Sep 30 2022 10:57:08.952 (1664503028.952)
End:               Sep 30 2022 10:57:18.554 (1664503038.554)
Messages:          194
Topic information: Topic: /drive | Type: sensor_msgs/msg/Image | Count: 97 | Serialization Format: cdr
                Topic: /topic1 | Type: sensor_msgs/msg/Image | Count: 97 | Serialization Format: cdr

Record trace data#

  1. Open terminal to run a target application to record trace data with CARET

    In the launch file, use_sim_time is set to true and source nodes are disabled.

     source /opt/ros/humble/setup.bash
 source ~/ros2_caret_ws/install/local_setup.bash
 source ~/ros2_ws/install/local_setup.bash
 export LD_PRELOAD=$(readlink -f ~/ros2_caret_ws/install/caret_trace/lib/libcaret.so)

 ros2 launch caret_demos end_to_end_sample.launch.py use_sim_time:=true use_rosbag:=true

  2. Open another terminal to record the performance data with /clock topic.

     source /opt/ros/humble/setup.bash
 source ~/ros2_caret_ws/install/local_setup.bash
 source ~/ros2_ws/install/local_setup.bash

 ros2 caret record -s e2e_sample --record-clock

  3. Open another terminal to play the rosbag

     source /opt/ros/humble/setup.bash
 source ~/ros2_caret_ws/install/local_setup.bash
 source ~/ros2_ws/install/local_setup.bash

 ros2 bag play rosbag2_2022_09_30-10_57_06 --clock -r 0.2

  4. Stop the application and the rosbag

  5. Check if /clock topic is recorded in trace data as sim_time

    babeltrace ~/ros2_ws/evaluate/e2e_sample | cut -d' ' -f 4 | sort -u | grep sim_time
ros2_caret:sim_time:

Visualize results using sim_time#

  1. Launch Jupyter Notebook in ~/ros2_ws/evaluate and run the following scripts 
from bokeh.plotting import output_notebook
output_notebook()
from caret_analyze import Architecture, Application, Lttng
from caret_analyze.plot import Plot, message_flow

# Read trace data
arch = Architecture('lttng', './e2e_sample')
lttng = Lttng('./e2e_sample')

# Search and add path
paths = arch.search_paths(
    '/filter_node',
    '/message_driven_node')
arch.add_path('target_path', paths[0])
app = Application(arch, lttng)

# Draw message_flow
path = app.get_path('target_path')
plot = Plot.create_message_flow_plot(path)
plot.show(xaxis_type='sim_time')

# Draw node info
node = app.get_node('/filter_node')
plot = Plot.create_period_timeseries_plot(node.callbacks)
plot.show(xaxis_type='sim_time')