SERVER-46437: Create baseline build variant for single task generated tasks

buildscripts/evergreen_generate_resmoke_tasks.py

@@ -857,7 +857,8 @@ class GenerateSubSuites(object):
         LOGGER.debug("Splitting tasks based on fallback",
                      fallback=self.config_options.fallback_num_sub_suites)
         self.test_list = self.list_tests()
-        num_suites = min(self.config_options.fallback_num_sub_suites, len(self.test_list))
+        num_suites = min(self.config_options.fallback_num_sub_suites, len(self.test_list),
+                         self.config_options.max_sub_suites)
         suites = [Suite(self.config_options.suite) for _ in range(num_suites)]
         for idx, test_file in enumerate(self.test_list):
             suites[idx % num_suites].add_test(test_file, 0)

buildscripts/tests/test_evergreen_generate_resmoke_tasks.py

@@ -78,6 +78,7 @@ class TestAcceptance(unittest.TestCase):
             "project": "mongodb-mongo-master",
             "task_id": "task314",
             "task_name": "some_task_gen",
+            "max_sub_suites": 100,
         }
 
     @staticmethod
@@ -811,11 +812,12 @@ class EvergreenConfigGeneratorTest(unittest.TestCase):
 
 class GenerateSubSuitesTest(unittest.TestCase):
     @staticmethod
-    def get_mock_options(n_fallback=2):
+    def get_mock_options(n_fallback=2, max_sub_suites=100):
         options = MagicMock()
         options.target_resmoke_time = 10
         options.fallback_num_sub_suites = n_fallback
         options.max_tests_per_suite = None
+        options.max_sub_suites = max_sub_suites
         return options
 
     @staticmethod
@@ -861,6 +863,24 @@ class GenerateSubSuitesTest(unittest.TestCase):
 
         self.assertEqual(n_tests, len(gen_sub_suites.test_list))
 
+    def test_max_sub_suites_overrides_fallback(self):
+        n_tests = 100
+        n_fallback = 5
+        max_sub_suites = 1
+        evg = mock_test_stats_unavailable(MagicMock())
+        config_options = self.get_mock_options(n_fallback=n_fallback, max_sub_suites=max_sub_suites)
+
+        gen_sub_suites = under_test.GenerateSubSuites(evg, config_options)
+        gen_sub_suites.list_tests = MagicMock(return_value=self.get_test_list(n_tests))
+
+        suites = gen_sub_suites.calculate_suites(_DATE, _DATE)
+
+        self.assertEqual(max_sub_suites, len(suites))
+        for suite in suites:
+            self.assertEqual(n_tests, len(suite.tests))
+
+        self.assertEqual(n_tests, len(gen_sub_suites.test_list))
+
     def test_calculate_suites_more_fallback_suites_than_tests(self):
         n_tests = 5
         n_fallback = 10

etc/evergreen.yml

@@ -9990,7 +9990,7 @@ buildvariants:
   - enterprise
   run_on:
   - rhel62-small
-  expansions:
+  expansions: &enterprise-rhel-62-64-bit-expansions
     additional_targets: archive-mongocryptd archive-mongocryptd-debug
     push_path: linux
     push_bucket: downloads.10gen.com
@@ -10459,6 +10459,48 @@ buildvariants:
     - name: snmp
     - name: .updatefuzzer
 
+# The following build variant is meant to provide a baseline to measure how much overhead we
+# are spending when we split tasks into multiple sub-tasks.
+- name: enterprise-rhel-62-64-bit-single-task-baseline
+  display_name: "Enterprise RHEL 6.2 (Single Task Baseline)"
+  batchtime: 10080  # 1 week.
+  modules:
+    - enterprise
+  run_on:
+    - rhel62-small
+  expansions:
+    <<: *enterprise-rhel-62-64-bit-expansions
+    max_sub_suites: 1  # Only generate 1 sub-suite per task.
+  tasks:
+    - name: compile_all_run_unittests_TG
+      distros:
+        - rhel62-large
+    - name: .aggregation
+    - name: .auth
+    - name: unittest_shell_hang_analyzer_gen
+    - name: .causally_consistent !.sharding
+    - name: .change_streams
+    - name: .misc_js
+    - name: .encrypt
+    - name: .jscore .common
+    - name: .logical_session_cache
+    - name: .multi_shard
+    - name: multi_stmt_txn_jscore_passthrough_with_migration_gen
+    - name: multiversion_gen
+    - name: .read_write_concern .large
+      distros:
+        - rhel62-large
+    - name: .read_write_concern !.large
+    - name: .replica_sets !.encrypt !.auth
+      distros:
+        - rhel62-large
+    - name: retryable_writes_jscore_passthrough_gen
+    - name: .read_only
+    - name: .sharding .jscore !.wo_snapshot !.multi_stmt
+    - name: .sharding .txns
+    - name: .sharding .common
+    - name: secondary_reads_passthrough_gen
+
 - &enterprise-rhel-70-64-bit-template
   name: enterprise-rhel-70-64-bit
   display_name: "* Enterprise RHEL 7.0"