From 624345b4962ca96dc0a009397bcee14b0e4fbf6b Mon Sep 17 00:00:00 2001
From: Nikola Dipanov <ndipanov@redhat.com>
Date: Thu, 4 Jun 2015 17:09:13 +0100
Subject: libvirt: Don't try to confine a non-NUMA instance

Even though it seemed like a good idea at the time, it turns out that
choosing a NUMA node at random can lead to placements that are
suboptimal.

Since the benefit of the current approach is unclear, and the downside
is actually hurting users - it is best to remove it (we would be no
worse off than before Nova was even NUMA aware), and think about
optimizitaions going forward, if any.

Change-Id: Idd4d5c236067fc40ed3a5049f3c1a58b75f9b5e5
Closes-bug: #1461777
(cherry picked from commit eb253255d74cbe6e630225080c463f1eb16b9932)
Conflicts:
	nova/tests/unit/virt/libvirt/test_driver.py
	nova/virt/libvirt/driver.py
---
 nova/tests/virt/libvirt/test_driver.py | 13 ++++---------
 nova/virt/libvirt/driver.py            | 30 ++++++------------------------
 2 files changed, 10 insertions(+), 33 deletions(-)

diff --git a/nova/tests/virt/libvirt/test_driver.py b/nova/tests/virt/libvirt/test_driver.py
index 60acd651a2..571bc1be5d 100644
--- a/nova/tests/virt/libvirt/test_driver.py
+++ b/nova/tests/virt/libvirt/test_driver.py
@@ -1209,11 +1209,9 @@ class LibvirtConnTestCase(test.TestCase):
                     objects.Flavor, "get_by_id", return_value=flavor),
                 mock.patch.object(conn, '_has_min_version', return_value=True),
                 mock.patch.object(
-                    conn, "_get_host_capabilities", return_value=caps),
-                mock.patch.object(
-                        random, 'choice', side_effect=lambda cells: cells[0])):
+                    conn, "_get_host_capabilities", return_value=caps)):
             cfg = conn._get_guest_config(instance_ref, [], {}, disk_info)
-            self.assertEqual(set([0, 1]), cfg.cpuset)
+            self.assertIsNone(cfg.cpuset)
             self.assertIsNone(cfg.cputune)
             self.assertIsNone(cfg.cpu.numa)
 
@@ -1272,15 +1270,12 @@ class LibvirtConnTestCase(test.TestCase):
                 mock.patch.object(
                     conn, "_get_host_capabilities", return_value=caps),
                 mock.patch.object(
-                    hardware, 'get_vcpu_pin_set', return_value=set([2, 3])),
-                mock.patch.object(
-                    random, 'choice', side_effect=lambda cells: cells[0])
+                    hardware, 'get_vcpu_pin_set', return_value=set([2, 3]))
                 ) as (get_by_id_mock, has_min_version_mock, get_host_cap_mock,
-                        get_vcpu_pin_set_mock, choice_mock):
+                        get_vcpu_pin_set_mock):
             cfg = conn._get_guest_config(instance_ref, [], {}, disk_info)
             # NOTE(ndipanov): we make sure that pin_set was taken into account
             # when choosing viable cells
-            choice_mock.assert_called_once_with([set([2, 3])])
             self.assertEqual(set([2, 3]), cfg.cpuset)
             self.assertIsNone(cfg.cputune)
             self.assertIsNone(cfg.cpu.numa)
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 9c67f3515a..c26546b264 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -31,7 +31,6 @@ import functools
 import glob
 import mmap
 import os
-import random
 import shutil
 import socket
 import sys
@@ -3753,29 +3752,12 @@ class LibvirtDriver(driver.ComputeDriver):
                 context, instance)
 
         if not guest_cpu_numa:
-            # No NUMA topology defined for instance
-            vcpus = flavor.vcpus
-            memory = flavor.memory_mb
-            if topology:
-                # Host is NUMA capable so try to keep the instance in a cell
-                viable_cells_cpus = []
-                for cell in topology.cells:
-                    if vcpus <= len(cell.cpuset) and memory <= cell.memory:
-                        viable_cells_cpus.append(cell.cpuset)
-
-                if not viable_cells_cpus:
-                    # We can't contain the instance in a cell - do nothing for
-                    # now.
-                    # TODO(ndipanov): Attempt to spread the instance accross
-                    # NUMA nodes and expose the topology to the instance as an
-                    # optimisation
-                    return allowed_cpus, None, None
-                else:
-                    pin_cpuset = random.choice(viable_cells_cpus)
-                    return pin_cpuset, None, None
-            else:
-                # We have no NUMA topology in the host either
-                return allowed_cpus, None, None
+            # No NUMA topology defined for instance - let the host kernel deal
+            # with the NUMA effects.
+            # TODO(ndipanov): Attempt to spread the instance
+            # across NUMA nodes and expose the topology to the
+            # instance as an optimisation
+            return allowed_cpus, None, None
         else:
             if topology:
                 # Now get the CpuTune configuration from the numa_topology
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