plugin: get cpu_count from sched_getaffinity

Signed-off-by: Yoan Blanc <yoan.blanc@exoscale.ch>

changelog/9.bugfix

@@ -0,0 +1 @@
+Fix issue of virtualized or containerized environments not reporting the number of CPUs correctly

testing/test_plugin.py

@@ -31,7 +31,9 @@ def test_dist_options(testdir):
 
 def test_auto_detect_cpus(testdir, monkeypatch):
     import os
-    if hasattr(os, 'cpu_count'):
+    if hasattr(os, 'sched_getaffinity'):
+        monkeypatch.setattr(os, 'sched_getaffinity', lambda _pid: set(range(99)))
+    elif hasattr(os, 'cpu_count'):
         monkeypatch.setattr(os, 'cpu_count', lambda: 99)
     else:
         import multiprocessing

xdist/plugin.py

@@ -4,10 +4,16 @@ import pytest
 
 def parse_numprocesses(s):
     if s == 'auto':
+        try:
+            from os import sched_getaffinity
+            def cpu_count():
+                return len(sched_getaffinity(0))
+        except ImportError:
             try:
                 from os import cpu_count
             except ImportError:
                 from multiprocessing import cpu_count
+
         try:
             n = cpu_count()
         except NotImplementedError: