ubuntu_ftrace_smoke_test failed on D-aws a1.medium arm64 instance

Issue found on AWS ARM64 instance a1.medium, passed on the other 2 (a1.2xlarge / a1.large)

Test failed with:
   FAILED (irq traces found must be > 32, got 18)

PASSED (CONFIG_FUNCTION_TRACER=y in /boot/config-5.0.0-1011-aws)
PASSED (CONFIG_FUNCTION_GRAPH_TRACER=y in /boot/config-5.0.0-1011-aws)
PASSED (CONFIG_STACK_TRACER=y in /boot/config-5.0.0-1011-aws)
PASSED (CONFIG_DYNAMIC_FTRACE=y in /boot/config-5.0.0-1011-aws)
PASSED all expected /sys/kernel/debug/tracing files exist
PASSED (function_graph in /sys/kernel/debug/tracing/available_tracers)
PASSED (function in /sys/kernel/debug/tracing/available_tracers)
PASSED (nop in /sys/kernel/debug/tracing/available_tracers)
PASSED (function can be enabled)
FAILED (irq traces found must be > 32, got 18)
PASSED (function_graph can be enabled)
PASSED (irq traces found must be > 32, got 9279)
PASSED (tracer hwlat can be enabled (got 12 lines of tracing output))
PASSED (tracer blk can be enabled (got 2 lines of tracing output))
PASSED (tracer function_graph can be enabled (got 1374 lines of tracing output))
PASSED (tracer wakeup_dl can be enabled (got 2 lines of tracing output))
PASSED (tracer wakeup_rt can be enabled (got 66 lines of tracing output))
PASSED (tracer wakeup can be enabled (got 64 lines of tracing output))
PASSED (tracer function can be enabled (got 757 lines of tracing output))
Summary: 18 passed, 1 failed

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: linux-image-5.0.0-1011-aws 5.0.0-1011.12
ProcVersionSignature: User Name 5.0.0-1011.12-aws 5.0.15
Uname: Linux 5.0.0-1011-aws aarch64
ApportVersion: 2.20.10-0ubuntu27.1
Architecture: arm64
Date: Thu Aug 8 10:56:19 2019
Ec2AMI: ami-0ac1a3bc4f5c85238
Ec2AMIManifest: (unknown)
Ec2AvailabilityZone: us-west-2c
Ec2InstanceType: a1.medium
Ec2Kernel: unavailable
Ec2Ramdisk: unavailable
SourcePackage: linux-aws
UpgradeStatus: No upgrade log present (probably fresh install)