Test Round-trip Time

The test_rtt node-type is a virtual node-type which can be used to measure round-trip time to other nodes. The test_rtt nodes periodically generate probes which must be looped back via a second node.

Hint for raw format

If your second node is using the raw format you will need to set the fake = true setting in the format configuration.

Otherwise, no sample meta data such as time stamps are exchanged. However, these are required by the test_rtt node-type to calculate the round-trip time.

Prerequisites

This node-type does not have any special library dependencies. It is always available.

Implementation

The source code of the node-type is available here: https://github.com/VILLASframework/node/blob/master/lib/nodes/test_rtt.cpp

Configuration

	Format Object (object) or Format Name (string) (format_spec)
prefix	string A prefix which is prepended to the output file name of the RTT test result file.
output	string Default: "." A directory path at which the RTT test result files be placed.
cooldown	number Default: 0 A cool-down time between consecutive test cases. The node will insert a pause between the tests to avoid any network effects of the previous test-case to influence the upcoming test-case.
required	object A list of test-case specifications. The values from the rates and values settings of each-test case specification will be used to form a cross-product.
vectorize	integer Default: 1 This setting allows to send multiple samples in a single message to the destination nodes. The value of this setting determines how many samples will be combined into one packet.
	Array of Hook Object (object) or Hook Name (string) (hook_list)
builtin	boolean (Builtin hook functions) Default: true By default, each node and paths has a couple of default hooks attached to them. With this setting the attachment of built-in hooks can be disabled.
	object (Input configuration (received by VILLASnode))
	object (Output configuration (sent out by VILLASnode))

{

• "format": "villas.human",
• "prefix": "test_1",
• "output": ".",
• "cooldown": 0,
• "cases": {

  • "rates": [

    • 10,
    • 100,
    • 1000,
    • 10000

    ],
  • "values": [

    • 10,
    • 100

    ],
  • "count": 10000,
  • "duration": 60,
  • "mode": "min"

  },
• "vectorize": 1,
• "hooks": [

  • "print",
  • {

    • "type": "limit_rate",
    • "rate": 1000

    }

  ],
• "builtin": true,
• "in": {

  • "vectorize": 1,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  },
• "out": {

  • "vectorize": 0,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  }

}

Example

node/etc/examples/nodes/test_rtt.conf

nodes = {

    # The "test_rtt" node-type runs a set of test cases for varying
    # sending rates, number of values and generates statistics
    # The cooldown time between each test case in seconds
    rtt_node = {
        type = "test_rtt"
        cooldown = 2

        # An optional prefix in the filename
        prefix = "test_rtt_%y-%m-%d_%H-%M-%S"

        # The output directory for all results
        # The results of each test case will be written to a separate file
        output = "./results"

        # The output format of the result files
        format = "villas.human"

        # Shutdown the process after the cooldown phase of the
        # last test case has been completed.
        shutdown = true;

        # One of:
        # - min
        # - max
        # - at_least_count
        # - at_least_duration
        # - stop_after_count
        # - stop_after_duration
        mode = "at_least_count"

        # The list of test cases
        # Each test case can specify a single or an array of rates and values
        # If arrays are used, we will generate multiple test cases with all
        # possible combinations
        cases = (
            {
                # The sending rate in Hz
                rates = 55.0

                # The number of values which should be send in each sample
                values = [ 5, 10, 20]

                # The number of samples which should be send during this test case
                count = 100
            },
            {
                # An array of sending rates in Hz
                rates = [ 5, 10, 30 ]

                # An array of number of values
                values = [ 2, 10, 20 ]

                # The duration of the test case in seconds (depending on the sending rate)
                duration = 5
            }
        )
    }
}