Set nohz_full in cpu-pinning element

nohz_full (or full dynticks) is a Linux kernel setting that should reduce
kernel noise on configured CPUs to a minimum. This change activates this
setting on all vCPUs except the first one.

Change-Id: Ie009aff52d572873da0bb5cc43fedd7f3325dccc

Author: weinimo

elements/cpu-pinning/environment.d/80-kernel-cpu-affinity

@@ -27,6 +27,7 @@ case $DISTRO_NAME in
         DIB_BOOTLOADER_DEFAULT_CMDLINE+=" irqaffinity=0"
         # This will be ignored on single vCPU systems
         DIB_BOOTLOADER_DEFAULT_CMDLINE+=" isolcpus=1-N"
+        DIB_BOOTLOADER_DEFAULT_CMDLINE+=" nohz=on nohz_full=1-N"
         export DIB_BOOTLOADER_DEFAULT_CMDLINE
     ;;
     *)

releasenotes/notes/use-nohz-full-to-improve-latency-9d5acd7333f7e462.yaml

@@ -0,0 +1,13 @@
+---
+features:
+  - |
+    The cpu-pinning element for the amphora image sets the kernel bootarg
+    nohz_full=1-N to enable
+    full dynticks on all CPUs except the first one (on single CPU images this
+    will have no effect). This should reduce kernel noise on those CPUs to a
+    minimum and reduce latency.
+upgrade:
+  - |
+    In order for the full dynticks optimization to become effective a new 
+    amphora image needs to be built with the new optional CPU pinning 
+    feature enabled.