Bug 1772894
| Summary: | kvm nx_huge_pages_recovery_ratio=0 is needed to meet KVM-RT low latency requirement | |||
|---|---|---|---|---|
| Product: | Red Hat Enterprise Linux 7 | Reporter: | Paolo Bonzini <pbonzini> | |
| Component: | kernel-rt | Assignee: | Tom Rix <trix> | |
| kernel-rt sub component: | KVM | QA Contact: | Pei Zhang <pezhang> | |
| Status: | CLOSED ERRATA | Docs Contact: | ||
| Severity: | high | |||
| Priority: | high | CC: | bhu, chayang, dhoward, jinzhao, juzhang, knoel, lgoncalv, lilu, lmiksik, pbonzini, peterx, pezhang, trix, virt-bugs, 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: | 1772738 | |||
| : | 1781156 1781157 (view as bug list) | Environment: | ||
| Last Closed: | 2020-03-31 19:51:08 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: | 1772738 | |||
| Bug Blocks: | 1672377, 1715542, 1779458, 1781156, 1781157 | |||
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Comment 2
Beth Uptagrafft
2019-11-15 15:57:59 UTC
*** Bug 1779455 has been marked as a duplicate of this bug. *** The mitigation itself does not cause jitter, it only slows down the guest somewhat. Real-time is not about running things fast, but "fast enough" and predictably. (In reply to Paolo Bonzini from comment #14) > The mitigation itself does not cause jitter, it only slows down the guest > somewhat. Real-time is not about running things fast, but "fast enough" and > predictably. Makes sense. Sorry I confused with this - of course we can't turn off a mitigation by default. Then we probably need to add kvm.nx_huge_pages=0 manually when testing with all mitigations=off case for kvm-rt, because IIUC otherwise the guest could stop to use huge pages on some page table entries witout notice. Mitigations=off already disables nx_huge_pages=0 so we're safe for that. *** Bug 1779455 has been marked as a duplicate of this bug. *** Verified with kernel-rt-3.10.0-1125.rt56.1091.el7.x86_64:
1. Default nx_huge_pages_recovery_ratio is 0. This is expected.
# systool -vm kvm | grep nx_hug
nx_huge_pages_recovery_ratio= "0"
nx_huge_pages = "Y"
2. KVM-RT acceptance get PASS. 1 hour cyclictest max latency is 21us.
==Results==
(1)Single VM with 1 rt vCPU:
# Min Latencies: 00006
# Avg Latencies: 00007
# Max Latencies: 00020
(2)Single VM with 8 rt vCPUs:
# Min Latencies: 00006 00008 00008 00008 00008 00008 00008 00008
# Avg Latencies: 00007 00008 00008 00008 00008 00008 00008 00008
# Max Latencies: 00021 00020 00019 00018 00018 00019 00019 00018
(3)Multiple VMs each with 1 rt vCPU:
- VM1
# Min Latencies: 00006
# Avg Latencies: 00007
# Max Latencies: 00020
- VM2
# Min Latencies: 00006
# Avg Latencies: 00007
# Max Latencies: 00018
- VM3
# Min Latencies: 00006
# Avg Latencies: 00007
# Max Latencies: 00019
- VM4
# Min Latencies: 00005
# Avg Latencies: 00007
# Max Latencies: 00018
==Versions==
qemu-kvm-tools-rhev-2.12.0-43.el7.x86_64
microcode_ctl-2.1-61.el7.x86_64
rt-tests-1.5-9.el7.x86_64
kernel-rt-3.10.0-1125.rt56.1091.el7.x86_64
qemu-kvm-rhev-2.12.0-43.el7.x86_64
qemu-kvm-common-rhev-2.12.0-43.el7.x86_64
tuned-2.11.0-8.el7.noarch
libvirt-4.5.0-32.el7.x86_64
Beaker job:https://beaker.engineering.redhat.com/jobs/4048311
So this bug has been fixed very well. Move to 'VERIFIED'.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2020:1070 |