Note: This bug is displayed in read-only format because the product is no longer active in Red Hat Bugzilla.

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Bug 1812944

Summary:	Request nx_huge_pages=N as default value to avoid kvm-rt guest large latency spike [rhel-7.6.z]
Product:	Red Hat Enterprise Linux 7	Reporter:	RAD team bot copy to z-stream <autobot-eus-copy>
Component:	kernel-rt	Assignee:	Tom Rix <trix>
kernel-rt sub component:	KVM	QA Contact:	Pei Zhang <pezhang>
Status:	CLOSED CURRENTRELEASE	Docs Contact:
Severity:	high
Priority:	high	CC:	bhu, chayang, dhoward, fherrman, jinzhao, juzhang, kernel-eus-qe, lcapitulino, lgoncalv, mstowell, mtosatti, nilal, pezhang, trix, virt-maint, williams
Version:	7.8	Keywords:	ZStream
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:	1788009	Environment:
Last Closed:	2020-04-15 15:57:01 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1788009
Bug Blocks:	1730479

Description RAD team bot copy to z-stream 2020-03-12 14:31:03 UTC

This bug has been copied from bug #1788009 and has been proposed to be backported to 7.6 z-stream (EUS).

Comment 7 Pei Zhang 2020-03-23 03:19:00 UTC

Verified with kernel-rt-3.10.0-957.48.1.rt56.966.el7.x86_64:

1. Default value of nx_huge_pages is N. This is expected.

# systool -vm kvm | grep nx_huge
    nx_huge_pages_recovery_ratio= "0"
    nx_huge_pages       = "N"

2. With mitigations off, 24h cyclictest max latency is 41us. We expect 20us, but I don't think the spike is caused by this bug, and Bug 1790469 is tracking it.

==Results==
(1)Single VM with 1 rt vCPU:
# Min Latencies: 00005
# Avg Latencies: 00006
# Max Latencies: 00020

(2)Single VM with 8 rt vCPUs:
# Min Latencies: 00005 00005 00005 00005 00005 00005 00005 00005
# Avg Latencies: 00006 00005 00005 00005 00005 00005 00005 00005
# Max Latencies: 00020 00017 00016 00017 00016 00021 00016 00016

(3)Multiple VMs each with 1 rt vCPU:
- VM1
# Min Latencies: 00005
# Avg Latencies: 00006
# Max Latencies: 00030

- VM2
# Min Latencies: 00005
# Avg Latencies: 00006
# Max Latencies: 00021

- VM3
# Min Latencies: 00005
# Avg Latencies: 00006
# Max Latencies: 00020

- VM4
# Min Latencies: 00005
# Avg Latencies: 00007
# Max Latencies: 00041

So this bug has been fixed. Move to 'VERIFIED'.