From 780d0e5f9707358a1f38dd6a181ab12a5c84a0f9 Mon Sep 17 00:00:00 2001
From: Martin Schuppert <mschuppert@redhat.com>
Date: Thu, 14 Jun 2018 16:35:46 +0200
Subject: [PATCH] Introduces NovaComputeCpuSharedSet parameter

New compute/cpu_shared_set nova config can be set via parameter
NovaComputeCpuSharedSet.

Some workloads run best when the hypervisor overhead processes
(emulator threads in libvirt/QEMU) can be placed on different
physical host CPUs than other guest CPU resources. This allow
those workloads to prevent latency spikes for guest vCPU threads.

A list or range of physical CPU cores to reserve for for best-
effort guest vCPU resources (e.g. emulator threads in libvirt/QEMU)
can be specified.

Closes-Bug: 1776905

Change-Id: I53c567e8eeef12d582205b6e2d8310635555b5b8
---
 puppet/services/nova-compute.yaml                | 12 ++++++++++++
 .../compute-cpu-shared-set-be9da772ac8f7582.yaml | 16 ++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 releasenotes/notes/compute-cpu-shared-set-be9da772ac8f7582.yaml

diff --git a/puppet/services/nova-compute.yaml b/puppet/services/nova-compute.yaml
index 8c64745236..bedef486b8 100644
--- a/puppet/services/nova-compute.yaml
+++ b/puppet/services/nova-compute.yaml
@@ -102,6 +102,16 @@ parameters:
     default: []
     tags:
       - role_specific
+  NovaComputeCpuSharedSet:
+    description: >
+      A list or range of physical CPU cores will be used for best-effort guest
+      vCPU resources (e.g. emulator threads in libvirt/QEMU).
+      Ex. NovaComputeCpuSharedSet: [4-12,^8,15] will reserve cores from 4-12
+      and 15, excluding 8.
+    type: comma_delimited_list
+    default: []
+    tags:
+      - role_specific
   NovaReservedHostMemory:
     description: >
       Reserved RAM for host processes.
@@ -172,10 +182,12 @@ resources:
         map_replace:
           - map_replace:
             - nova::compute::vcpu_pin_set: NovaVcpuPinSet
+              nova::compute::cpu_shared_set: NovaComputeCpuSharedSet
               nova::compute::reserved_host_memory: NovaReservedHostMemory
             - values: {get_param: [RoleParameters]}
           - values:
               NovaVcpuPinSet: {get_param: NovaVcpuPinSet}
+              NovaComputeCpuSharedSet: {get_param: NovaComputeCpuSharedSet}
               NovaReservedHostMemory: {get_param: NovaReservedHostMemory}
 
 outputs:
diff --git a/releasenotes/notes/compute-cpu-shared-set-be9da772ac8f7582.yaml b/releasenotes/notes/compute-cpu-shared-set-be9da772ac8f7582.yaml
new file mode 100644
index 0000000000..c5d58ecb85
--- /dev/null
+++ b/releasenotes/notes/compute-cpu-shared-set-be9da772ac8f7582.yaml
@@ -0,0 +1,16 @@
+---
+features:
+  - |
+    Introduces NovaComputeCpuSharedSet parameter to set
+    ``[compute]/cpu_shared_set`` option for compute nodes.
+    Some workloads run best when the hypervisor overhead processes
+    (emulator threads in libvirt/QEMU) can be placed on different
+    physical host CPUs than other guest CPU resources. This allows
+    those workloads to prevent latency spikes for guest vCPU threads.
+
+    To place a workload's emulator threads on a set of isolated
+    physical CPUs, set the configuration option to the set of host
+    CPUs that should be used for best-effort CPU resources. Then set
+    a flavor extra spec to ``hw:emulator_threads_policy=share`` to
+    instruct nova to place that workload's emulator threads on that
+    set of host CPUs.