Parallelized service starting and stopping tasks

[Michael-Hollister]

Following up from parallelizing some of the tasks in the matrix-docker-ansible-deploy playbook, I have added the option to start/stop services asynchronously. Here are the following benchmarks when using this feature in the matrix-docker-ansible-deploy playbook:

Benchmarks

start-all

Number of Services	Before (synchronous)	After (async)
45	3m 2s	1m 29s (51% improvement)
123	8m 42s	5m 45s (34% improvement)

stop-all

Number of Services	Before (synchronous)	After (async)
45	1m 56s	53s (54% improvement)
123	6m 28s	4m 10s (35% improvement)

Ansible controller CPU: Ryzen 5900X

Also observed faster results by using more jobs for the host configuration using 123 services, but the results above used the default value of devture_systemd_service_manager_parallel_jobs: 16

Comments

I have left this feature disabled by default however for the following reasons:

• Don't know if Window's shell support is required for this role (xargs usage)
• Easier debugging of task failure with parallelization turned off
• Strict priority starting/stopping ordering is not followed since services are started/stopped in parallel. I did test implementations that respected service priority for starting/stopping services, but its slower and more complex code-wise.