Two Ways Test

About

• Check Real-Time performance by following scenarios:
  • ping-pong
• ping-pong is implemented by 2 topics with following publisher and subscriber.
  • ping-publisher(ping-pub) sends ping periodically using ping-topic.
  • ping-subscriber(ping-sub) and pong-publisher(pong-pub) ping-sub subscribes ping-topic and optionally pong-pub sends pong by pong-topic.
  • pong-subscriber(pong-sub) subscribes pong-topic.
• There are some variations for the number of Executors and Nodes, e.g.
  • 1 Executor 1 Node
  • 1 Executor 2 Node
    • Node1 contains ping-pub + pong_sub
    • Node2 contains ping-sub + pong-pub
  • seperate above 2 Node into 2 Executors
• Service version ping-pong is also implemented but obsolute.

Environment

• Ubuntu 18.04
  • If you want to run with scheduling option etc, you must run as root.
• ROS 2 Foxy

Build

# This has many sub packages
colcon list

# build all
colcon build --symlink-install

# build what you want
colcon build --symlink-install --packages-up-to tw_ping_pong

Run

# default option
./build/tw_topic/tw_ping_pong

# main-thread: RR98, child-thread: RR97, run-type 1e2n
./build/tw_topic/tw_ping_pong \
    --main-sched RR98 --child-sched RR97 \
	--run-type 1e2n \
    --ros-args --param num_loops:=1000 -param period_ns:=1000000

Available options

type	option	default value	comment
command option	--sched-rrts	off	use RR-TS scheduler(OBSOLUTE)
	--sched-rrrr	off	use RR-RR scheduler(OBSOLUTE)
	--ipm	off	use intra process manager(communication)
	--round-ns	1000	histogram bin width in [ns]
	--num-skip	10	skip first N event to prevent initial overhead
	--static-executor		use StaticSingleThreadedExecutor
	--main-sched	TS	scheduling policy of main thread, use RR98/RR97/TS
	--child-sched	TS	scheduling policy of child thread, use RR98/RR97/TS
	--run-type	1e1n	executor/node setting. see below
parameter	period_ns	10,000,000	timer period[ns]
	num_loops	10,000	number of loops
	debug_print	false	print debug message

run-type

value	meaning
1e1n	1 executor, 1 node
1e2n	1 executor, 2 nodes
2e_ping	ping process in 2 executors
2e_pong	pong process in 2 executors

Common Output

• Processes outputs following log to stdout as following. They output "recent values" and "average" of some metrics.

wakeup_jitters recent values: 
  202076 211784 216894 219512 233099 ...
wakeup_jitters average: 255350
recv_jitters recent values: 
  234106 178137 168598 168912 181125 ...
recv_jitters average: 178862

Here are meanings. unit are [ns], but chrono::system_clock is used internally. As in https://cpprefjp.github.io/reference/chrono/system_clock.html, gcc has microseconds resolution.

name	value	unit
wakeup_jitters	ping-pub wake up time-diff between expected wake up time and actual.	[ns]
recv_jitters	time-diff between ping-pub send and ping-sub recv.	[ns]