15.4.2. Task Template Syntax

15.4.2.1. Basic template syntax

A nice feature of the input task format used in Yardstick is that it supports the template syntax based on Jinja2. This turns out to be extremely useful when, say, you have a fixed structure of your task but you want to parameterize this task in some way. For example, imagine your input task file (task.yaml) runs a set of Ping scenarios:

# Sample benchmark task config file
# measure network latency using ping
schema: "yardstick:task:0.1"

scenarios:
-
  type: Ping
  options:
    packetsize: 200
  host: athena.demo
  target: ares.demo

  runner:
    type: Duration
    duration: 60
    interval: 1

  sla:
    max_rtt: 10
    action: monitor

context:
    ...

Let’s say you want to run the same set of scenarios with the same runner/ context/sla, but you want to try another packetsize to compare the performance. The most elegant solution is then to turn the packetsize name into a template variable:

# Sample benchmark task config file
# measure network latency using ping

schema: "yardstick:task:0.1"
scenarios:
-
  type: Ping
  options:
    packetsize: {{packetsize}}
  host: athena.demo
  target: ares.demo

  runner:
    type: Duration
    duration: 60
    interval: 1

  sla:
    max_rtt: 10
    action: monitor

context:
    ...

and then pass the argument value for {{packetsize}} when starting a task with this configuration file. Yardstick provides you with different ways to do that:

1.Pass the argument values directly in the command-line interface (with either a JSON or YAML dictionary):

yardstick task start samples/ping-template.yaml
--task-args'{"packetsize":"200"}'

2.Refer to a file that specifies the argument values (JSON/YAML):

yardstick task start samples/ping-template.yaml --task-args-file args.yaml

15.4.2.2. Using the default values

Note that the Jinja2 template syntax allows you to set the default values for your parameters. With default values set, your task file will work even if you don’t parameterize it explicitly while starting a task. The default values should be set using the {% set ... %} clause (task.yaml). For example:

# Sample benchmark task config file
# measure network latency using ping
schema: "yardstick:task:0.1"
{% set packetsize = packetsize or "100" %}
scenarios:
-
  type: Ping
  options:
  packetsize: {{packetsize}}
  host: athena.demo
  target: ares.demo

  runner:
    type: Duration
    duration: 60
    interval: 1
  ...

If you don’t pass the value for {{packetsize}} while starting a task, the default one will be used.

15.4.2.3. Advanced templates

Yardstick makes it possible to use all the power of Jinja2 template syntax, including the mechanism of built-in functions. As an example, let us make up a task file that will do a block storage performance test. The input task file (fio-template.yaml) below uses the Jinja2 for-endfor construct to accomplish that:

#Test block sizes of 4KB, 8KB, 64KB, 1MB
#Test 5 workloads: read, write, randwrite, randread, rw
schema: "yardstick:task:0.1"

 scenarios:
{% for bs in ['4k', '8k', '64k', '1024k' ] %}
  {% for rw in ['read', 'write', 'randwrite', 'randread', 'rw' ] %}
-
  type: Fio
  options:
    filename: /home/ubuntu/data.raw
    bs: {{bs}}
    rw: {{rw}}
    ramp_time: 10
  host: fio.demo
  runner:
    type: Duration
    duration: 60
    interval: 60

  {% endfor %}
{% endfor %}
context
    ...