From 73adde26e9f803ed87dbbc62a8be521ea45c71a1 Mon Sep 17 00:00:00 2001
From: Christopher Wilcox <git@crwilcox.com>
Date: Fri, 28 Jul 2017 09:42:07 -0700
Subject: [PATCH 1/3] Fixes #30581 by adding a path to use newer
 GetMaximumProcessorCount API on Windows calls to os.cpu_count()

---
 Modules/posixmodule.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index f4a21679d0b202..419c1ac47b2042 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -11128,9 +11128,22 @@ os_cpu_count_impl(PyObject *module)
 {
     int ncpu = 0;
 #ifdef MS_WINDOWS
-    SYSTEM_INFO sysinfo;
-    GetSystemInfo(&sysinfo);
-    ncpu = sysinfo.dwNumberOfProcessors;
+    /* Vista is supported and the GetMaximumProcessorCount API is Win7+
+       Need to fallback to Vista behavior if this call isn't present */
+    HINSTANCE hKernel32;
+    hKernel32 = GetModuleHandleW(L"KERNEL32");
+
+    static DWORD(CALLBACK *_GetMaximumProcessorCount)(WORD) = NULL;
+    *(FARPROC*)&_GetMaximumProcessorCount = GetProcAddress(hKernel32,
+        "GetMaximumProcessorCount");
+    if (_GetMaximumProcessorCount != NULL) {
+        ncpu = _GetMaximumProcessorCount(ALL_PROCESSOR_GROUPS);
+    }
+    else {
+        SYSTEM_INFO sysinfo;
+        GetSystemInfo(&sysinfo);
+        ncpu = sysinfo.dwNumberOfProcessors;
+    }
 #elif defined(__hpux)
     ncpu = mpctl(MPC_GETNUMSPUS, NULL, NULL);
 #elif defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)

From ef1b70469a53fd705fbe8f030d83800bd3d48f93 Mon Sep 17 00:00:00 2001
From: Christopher Wilcox <git@crwilcox.com>
Date: Fri, 4 Aug 2017 10:06:07 -0700
Subject: [PATCH 2/3] Add NEWS.d entry for bpo-30581, os.cpu_count on Windows.

---
 .../next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst       | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst

diff --git a/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
new file mode 100644
index 00000000000000..928a2623793457
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
@@ -0,0 +1,2 @@
+The behavior of os.cpu_count() has changed on Windows. Windows will never
+return, nor have access to, more than 32 CPUs on a 32 bit build of Python.

From 780ea3cc96bf35ca016fc62e5d4fccbc7ca8b004 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <pitrou@free.fr>
Date: Wed, 30 Aug 2017 10:44:24 +0200
Subject: [PATCH 3/3] Tweak NEWS entry

---
 .../next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst     | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
index 928a2623793457..6591fa0df00267 100644
--- a/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
+++ b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
@@ -1,2 +1,2 @@
-The behavior of os.cpu_count() has changed on Windows. Windows will never
-return, nor have access to, more than 32 CPUs on a 32 bit build of Python.
+os.cpu_count() now returns the correct number of processors on Windows
+when the number of logical processors is greater than 64.