Time the CPU tests on Jenkins. (#6257)

* Time the CPU tests on Jenkins.
* Reduce thread contention.
* Add doc.
* Skip heavy tests on ARM.

tests/python/test_demos.py

@@ -39,6 +39,7 @@ def test_feature_weights_demo():
 
 
 @pytest.mark.skipif(**tm.no_sklearn())
+@pytest.mark.skipif(**tm.is_arm())
 def test_sklearn_demo():
     script = os.path.join(PYTHON_DEMO_DIR, 'sklearn_examples.py')
     cmd = ['python', script]
@@ -48,6 +49,7 @@ def test_sklearn_demo():
 
 
 @pytest.mark.skipif(**tm.no_sklearn())
+@pytest.mark.skipif(**tm.is_arm())
 def test_sklearn_parallel_demo():
     script = os.path.join(PYTHON_DEMO_DIR, 'sklearn_parallel.py')
     cmd = ['python', script]

tests/python/test_early_stopping.py

@@ -83,6 +83,7 @@ class TestEarlyStopping(unittest.TestCase):
 
     @pytest.mark.skipif(**tm.no_sklearn())
     @pytest.mark.skipif(**tm.no_pandas())
+    @pytest.mark.skipif(**tm.is_arm())
     def test_cv_early_stopping_with_multiple_eval_sets_and_metrics(self):
         from sklearn.datasets import load_breast_cancer
 

tests/python/test_with_dask.py

@@ -611,10 +611,6 @@ class TestWithDask:
                          tree_method):
         params['tree_method'] = tree_method
         params = dataset.set_params(params)
-        # multi class doesn't handle empty dataset well (empty
-        # means at least 1 worker has data).
-        if params['objective'] == "multi:softmax":
-            return
         # It doesn't make sense to distribute a completely
         # empty dataset.
         if dataset.X.shape[0] == 0:
@@ -640,18 +636,20 @@ class TestWithDask:
         # Make sure that it's decreasing
         assert history[-1] < history[0]
 
+    @pytest.mark.skipif(**tm.is_arm())
     @given(params=hist_parameter_strategy,
-           num_rounds=strategies.integers(20, 30),
            dataset=tm.dataset_strategy)
     @settings(deadline=None)
-    def test_hist(self, params, num_rounds, dataset, client):
+    def test_hist(self, params, dataset, client):
+        num_rounds = 30
         self.run_updater_test(client, params, num_rounds, dataset, 'hist')
 
+    @pytest.mark.skipif(**tm.is_arm())
     @given(params=exact_parameter_strategy,
-           num_rounds=strategies.integers(20, 30),
            dataset=tm.dataset_strategy)
     @settings(deadline=None)
-    def test_approx(self, client, params, num_rounds, dataset):
+    def test_approx(self, client, params, dataset):
+        num_rounds = 30
         self.run_updater_test(client, params, num_rounds, dataset, 'approx')
 
     def run_quantile(self, name):

tests/python/testing.py

@@ -1,5 +1,6 @@
 # coding: utf-8
 import os
+import platform
 from xgboost.compat import SKLEARN_INSTALLED, PANDAS_INSTALLED
 from xgboost.compat import DASK_INSTALLED
 import pytest
@@ -22,6 +23,10 @@ except ImportError:
 memory = Memory('./cachedir', verbose=0)
 
 
+def is_arm():
+    return {'condition': platform.machine().lower().find('arm') != 1,
+            'reason': 'Skipping expensive tests on ARM.'}
+
 def no_sklearn():
     return {'condition': not SKLEARN_INSTALLED,
             'reason': 'Scikit-Learn is not installed'}