Changes:

	- implement the TestTask.overhead property that returns a float value representing non-group time.
	- add new query to obtain start/end times for the group and task.

mozci/queries/test_task_overhead.query

@@ -0,0 +1,11 @@
+from: unittest
+format: list
+groupby: task.id
+limit: 20000
+select:
+    - {value: action.start_time, name: task_min, aggregate: min}
+    - {value: action.end_time, name: task_max, aggregate: max}
+    - {value: result.start_time, name: group_min, aggregate: min}
+    - {value: result.end_time, name: group_max, aggregate: max}
+where:
+    - in: {task.id: {$eval: task_id}}

mozci/task.py

@@ -2,13 +2,15 @@
 import json
 import os
 from abc import ABC, abstractmethod
+from argparse import Namespace
 from dataclasses import dataclass, field
 from enum import Enum
 from inspect import signature
 from statistics import median
 from typing import Dict, List, Optional
 
 import requests
+from adr.query import run_query
 from adr.util import memoized_property
 from loguru import logger
 from urllib3.response import HTTPResponse
@@ -358,6 +360,30 @@ def configuration(self):
         parts = config.split("-")
         return "-".join(parts[:-1] if parts[-1].isdigit() else parts)
 
+    @property
+    def overhead(self):
+        """Calculate the overhead of a task.
+
+        The methodology is simple: each task (action) has a start/end time.
+        Each group also has a start/end time. Take the earlist known group start
+        and latest known group end time, ensure the two falls somewhere in between
+        task start/end.
+
+        Then calculate the overhead by taking the difference between the start
+        and end times.
+
+        Returns:
+            float: difference between task start/end and group star/end times.
+        """
+        data = run_query("test_task_overhead", Namespace(task_id=self.id))["data"].pop()
+        # Sanity check to ensure group start/end times are within task start/end.
+        assert data["task_min"] < data["group_min"]
+        assert data["task_max"] > data["group_max"]
+
+        return (data["group_min"] - data["task_min"]) + (
+            data["task_max"] - data["group_max"]
+        )
+
 
 # Don't perform type checking because of https://github.com/python/mypy/issues/5374.
 @dataclass  # type: ignore