# Performance comparison between beluga_amcl and nav2_amcl

## Environment details

- CPU: **Intel(R) Core(TM) i9-9900 CPU @ 3.10GHz x 16 cores**
- CPU Caches: L1 Data 32 KiB (x8), L1 Instruction 32 KiB (x8), L2 Unified 256 KiB (x8), L3 Unified 16384 KiB (x1)
- RAM: 16384 MB
- Host OS: Ubuntu 22.04.6 LTS
- ROS 2 version: **Humble Hawksbill**
- AMCL version: `ros-humble-nav2-amcl` package, version 1.1.9-1jammy.20230807.174459

## Experimental setup

The following configuration was used during the experiments:

- The benchmarks were run using 250, 300, 400, 500, 750, 1000, 2000, 5000, 10000, 20000, 50000, 100000 and 200000 particles.
- `beluga_amcl` was run both using multi-threaded (`par`) and single-threaded (`seq`) configurations. `nav2_amcl` only provides single-threaded execution.
- Both the `beam sensor` and the `likelihood field` sensor model were tested.
- The bagfile containing the synthetic dataset was replayed at 1x speed (real time).

More specific configuration details can be found in the `yaml` files in the `baseline_configurations/` folder:

- `nav2_amcl` (likelihood field) uses [likelihood_params.yaml](likelihood_params.yaml)
- `beluga_amcl` (likelihood field, single-threaded) uses [likelihood_params.yaml](likelihood_params.yaml)
- `beluga_amcl` (likelihood field, multi-threaded) uses [likelihood_params_par.yaml](likelihood_params_par.yaml)
- `nav2_amcl` (beam) uses [beam_params.yaml](beam_params.yaml)
- `beluga_amcl` (beam, single-threaded) uses [beam_params.yaml](beam_params.yaml)
- `beluga_amcl` (beam, multi-threaded) uses [beam_params_par.yaml](beam_params_par.yaml)

Except for the multithreading and sensor model parameters, the configuration on all of the files is identical.

## Recorded metrics

The following metrics were recorded during each run:

- RSS (Resident Set Size), amount of memory alloated to the process. Measured in megabytes.
- CPU usage. Measured in percentage of the total CPU usage.
- rms APE (root-mean-squared Absolute Pose Error) statistics. In meters.
- Processing latency (time interval between laser-scan reception and pose estimation). Measured in milliseconds.

The processing latency was only recorded for `beluga_amcl`. The unmodified `nav2_amcl` binary does not provide this metric in the process output.

## Results

#### Beluga vs. Nav2 AMCL using Likelihood Field sensor model

In the following plot the results of the benchmark are shown for all three of the tested alternatives. The vertical scale is logarithmic to better show the differences between the configurations throughout the whole range of particle counts.

![Beluga Seq vs Beluga Par vs. Nav2 AMCL with Likelihood Field Sensor Model](likelihood_beluga_vs_beluga_vs_amcl.png)

Comments on the results:

- The memory usage of `beluga_amcl` (single and multi-threaded) is significantly lower than that of `nav2_amcl`.
- Both `beluga_amcl` configurations have a lower CPU load than `nav2_amcl` when using the `likelihood` sensor model. The multi-threaded configuration of `beluga_amcl` causes more CPU load than the single-threaded one due to the additional synchronization overhead.
- Above $50k$ particles `nav2_amcl` single-threaded process begins to saturate the CPU and its APE metrics begin to deteriorate, while `beluga_amcl` in both configurations remains stable thanks to its lower CPU load. For particle counts below $50k$ the APE metrics of all three alternatives are similar.
- The multi-threaded configuration of `beluga_amcl` has lower latency than the single-threaded one, at the expense of additional CPU load. The latency of `nav2_amcl` was not measured for the reasons explained above.

#### Beluga vs. Nav2 AMCL using Beam sensor model

In the following plot the results of the benchmark are shown for all three of the tested configurations when using the Beam Sensor model. The vertical scale is logarithmic to better show the differences between the configurations throughout the whole range of particle counts.

![Beluga Seq vs Beluga Par vs. Nav2 AMCL with Beam Sensor Model](beam_beluga_vs_beluga_vs_amcl.png)

Comments on the results:

- `beluga_amcl` in both multi-threaded and single-threaded configurations uses significantly less memory than `nav2_amcl`.
- Both the single-threaded configuration of `beluga_amcl` and `nav2_amcl` have similar CPU load performance when using the `beam` sensor model. The multi-threaded configuration of `beluga_amcl` uses more CPU than the single-threaded one due to the additional synchronization overhead.
- Above $50k$ particles both `nav2_amcl` and the single-threaded configuration of `beluga_amcl` begin to saturate the CPU and their APE metrics begin to deteriorate, while `beluga_amcl` in multi-threaded configuration remains stable. For particle counts below $50k$ the APE metrics of all three alternatives are similar.
- The multi-threaded configuration of `beluga_amcl` has lower latency than the single-threaded one, at the expense of additional CPU load. The latency of `nav2_amcl` was not measured for the reasons explained above.

## Conclusions

- `beluga_amcl`'s memory usage is significantly lower than that of `nav2_amcl` in all configurations.
- The single-threaded configuration of `beluga_amcl` performs at a lower or equal CPU load than that of `nav2_amcl`. When configured to use the `likelihood` sensor model the performance of the single-threaded `beluga_amcl` configuration is significantly better than that of `nav2_amcl`.
- The multi-threaded configuration of `beluga_amcl` always uses more CPU than the single-threaded configuration.
- `beluga_amcl`'s APE performance is similar to that of `nav2_amcl` for lower particle counts. For higher particle counts the performance begins to deteriorate when the processes saturate the available CPU resources.
- The multi-threaded configuration of `beluga_amcl` has lower latency than the single-threaded one, at the expense of additional CPU load. Also, Thanks to the reduced latency and higher CPU saturation ceiling the localization solution using `beluga_amcl` in multi-threaded configuration remains stable for higher particle counts.

## How to reproduce

To replicate the benchmarks, after building and sourcing the workspace, run the following commands from the current directory:

```bash
mkdir beam_beluga_seq
cd beam_beluga_seq
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000  --params-file $(pwd)/../../baseline_configurations/beam_params.yaml
cd -
mkdir beam_beluga_par
cd beam_beluga_par
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000  --params-file $(pwd)/../../baseline_configurations/beam_params_par.yaml
cd -
mkdir beam_nav2_amcl
cd beam_nav2_amcl
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000 --params-file $(pwd)/../../baseline_configurations/beam_params.yaml --package nav2_amcl --executable amcl
cd -
mkdir likelihood_beluga_seq
cd likelihood_beluga_seq
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000  --params-file $(pwd)/../../baseline_configurations/likelihood_params.yaml
cd -
mkdir likelihood_beluga_par
cd likelihood_beluga_par
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000  --params-file $(pwd)/../../baseline_configurations/likelihood_params_par.yaml
cd -
mkdir likelihood_nav2_amcl
cd likelihood_nav2_amcl
ros2 run beluga_benchmark parameterized_run --initial-pose-y 2.0 250 300 400 500 750 1000 2000 5000 10000 20000 50000 100000 200000 --params-file $(pwd)/../../baseline_configurations/likelihood_params.yaml --package nav2_amcl --executable amcl
cd -
```

Once the data has been acquired, it can be visualized using the following commands:

```bash
ros2 run beluga_benchmark compare_results \
    -s beam_beluga_seq -l beam_beluga_seq \
    -s beam_beluga_par -l beam_beluga_par \
    -s beam_nav2_amcl  -l beam_nav2_amcl --use-ylog

ros2 run beluga_benchmark compare_results \
    -s likelihood_beluga_seq -l likelihood_beluga_seq \
    -s likelihood_beluga_par -l likelihood_beluga_par \
    -s likelihood_nav2_amcl  -l likelihood_nav2_amcl --use-ylog
```