hdds-latency-probe

Measure DDS round-trip latency with a ping-pong benchmark.

Overview

hdds-latency-probe measures round-trip time (RTT) between two DDS participants using a ping-pong pattern. One host runs in ping mode (sender), the other in pong mode (echo responder). The tool reports detailed latency statistics including percentiles.

Installation

From Source

cd hdds/tools/hdds-latency-probe
cargo build --release

Binary at target/release/hdds-latency-probe.

From Cargo

cargo install hdds-latency-probe

Usage

hdds-latency-probe [OPTIONS] <COMMAND>

Commands:
  ping  Send ping messages and measure RTT
  pong  Echo back ping messages (run on remote host)

Global Options:
  -d, --domain <DOMAIN>  DDS domain ID [default: 0]
  -q, --qos <QOS>        QoS profile: best-effort, reliable [default: reliable]
  -h, --help             Print help
  -V, --version          Print version

Ping Mode Options

hdds-latency-probe ping [OPTIONS]

Options:
  -s, --size <SIZE>          Payload size in bytes [default: 64]
  -n, --count <COUNT>        Number of iterations (0 = unlimited) [default: 1000]
  -w, --warmup <WARMUP>      Warmup iterations before measurement [default: 10]
  -i, --interval <INTERVAL>  Interval between pings in microseconds [default: 1000]
      --json                 Output JSON results
      --quiet                Only output final results

Pong Mode Options

hdds-latency-probe pong [OPTIONS]

Options:
      --quiet  Quiet mode

Examples

Basic Latency Test

On the responder host:

hdds-latency-probe pong

On the sender host:

hdds-latency-probe ping

Output (sender):

>>> Latency probe (ping mode)
    domain=0, qos=Reliable, size=64 bytes, count=1000, warmup=10
    Waiting for pong responder...
    Warmup...
    Progress: 1000/1000

=== HDDS Latency Probe Results ===

  Payload size: 64 bytes
  Samples: 1000
  Lost: 0 (0.00%)
  Duration: 2.15s

--- Latency (microseconds) ---
  Min:         45.20 us
  Max:        312.80 us
  Mean:        78.45 us
  Stddev:      23.12 us

--- Percentiles ---
  p50:         72.30 us
  p90:        105.60 us
  p99:        198.40 us
  p99.9:      289.50 us

  Throughput: 465 msg/s

Different Payload Sizes

Test with larger messages:

hdds-latency-probe ping -s 1024    # 1 KB payload
hdds-latency-probe ping -s 65536   # 64 KB payload

More Samples

For better statistical accuracy:

hdds-latency-probe ping -n 10000

Faster Ping Rate

Reduce interval between pings (100 microseconds):

hdds-latency-probe ping -i 100

Skip Warmup

For quick tests:

hdds-latency-probe ping -w 0 -n 100

Best-Effort QoS

Lower latency but may lose samples:

# Both sides must use same QoS
hdds-latency-probe pong -q best-effort
hdds-latency-probe ping -q best-effort

JSON Output

For scripting and logging:

hdds-latency-probe ping --json

Output:

{"payload_size":64,"samples":1000,"lost":0,"duration_secs":2.154,"latency_us":{"min":45.20,"max":312.80,"mean":78.45,"stddev":23.12,"p50":72.30,"p90":105.60,"p99":198.40,"p999":289.50}}

Quiet Mode

One-line summary only:

hdds-latency-probe ping --quiet

Output:

min=45.2 max=312.8 avg=78.5 p99=198.4 us

Different Domain

hdds-latency-probe pong -d 42
hdds-latency-probe ping -d 42

Topics Used

The tool uses two internal topics:

• hdds_latency_ping - Ping messages (sender → responder)
• hdds_latency_pong - Pong responses (responder → sender)

Statistics Explained

Metric	Description
Min	Fastest round-trip observed
Max	Slowest round-trip observed
Mean	Average latency
Stddev	Standard deviation (jitter indicator)
p50	Median - 50% of samples below this
p90	90th percentile
p99	99th percentile - typical worst case
p99.9	99.9th percentile - rare outliers
Lost	Samples that didn't receive response within 1 second

Interpreting Results

Good Results

• p99 < 2x mean: Low jitter, stable network
• Lost = 0: Reliable delivery working
• Stddev < 50% of mean: Consistent latency

Warning Signs

• High p99.9 vs p99: Occasional spikes (GC, network congestion)
• Lost > 0 with Reliable QoS: Network issues or timeout too short
• Stddev > mean: Very high jitter

Typical Latencies

Environment	Expected RTT
Localhost (loopback)	20-50 µs
Same LAN (1 Gbps)	80-200 µs
Same LAN (10 Gbps)	40-100 µs
Cross-datacenter	1-10 ms
WiFi	0.5-5 ms

Comparison with Other Tools

Feature	hdds-latency-probe	iperf3	ping
Protocol	DDS/RTPS	TCP/UDP	ICMP
Application-level	Yes	No	No
Percentiles	Yes	No	No
Warmup phase	Yes	Yes	No
Payload size	Variable	Variable	Variable
QoS testing	Yes	No	No

Troubleshooting

No Response (100% Lost)

1. Ensure pong responder is running on remote host
2. Check domain IDs match
3. Check QoS profiles match (both reliable or both best-effort)
4. Verify multicast connectivity between hosts
5. Check firewall allows UDP ports 7400-7500

High Latency

1. Check network congestion
2. Try best-effort QoS (no ACK overhead)
3. Increase ping interval to reduce load
4. Check CPU usage on both hosts

High Jitter (Stddev)

1. Check for background processes
2. Disable CPU frequency scaling
3. Use real-time priority if available
4. Check for network packet loss

Exit Codes

Code	Meaning
0	Success
1	Error (DDS init failed, no responder, etc.)