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Bug 1817827 - "isolate_managed_irq=Y" should be mentioned in "/etc/tuned/realtime-virtual-*-variables.conf"
Summary: "isolate_managed_irq=Y" should be mentioned in "/etc/tuned/realtime-virtual-*...
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: tuned
Version: 8.2
Hardware: Unspecified
OS: Unspecified
low
low
Target Milestone: rc
: 8.5
Assignee: Jaroslav Škarvada
QA Contact: Robin Hack
URL:
Whiteboard:
Depends On:
Blocks: 1932086
TreeView+ depends on / blocked
 
Reported: 2020-03-27 03:42 UTC by Pei Zhang
Modified: 2021-11-10 10:03 UTC (History)
10 users (show)

Fixed In Version: tuned-2.16.0-0.1.rc1.el8
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2021-11-09 19:58:24 UTC
Type: Bug
Target Upstream Version:
Embargoed:
pm-rhel: mirror+

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2021:4476 0 None None None 2021-11-09 19:58:50 UTC

Description Pei Zhang 2020-03-27 03:42:21 UTC 
Description of problem:

"isolate_managed_irq=Y" is an important boolean option for rhel8.2 KVM-RT guest. Without this option, KVM-RT guest can not get expected latency performance.  

This option should be mentioned in the correct config files:  /etc/tuned/realtime-virtual-host-variables.conf (for RT host) and /etc/tuned/realtime-virtual-guest-variables.conf (for RT guest)

Current "isolate_managed_irq=Y" is only explained in /etc/tuned/realtime-variables.conf. This may confuse users.


Version-Release number of selected component (if applicable):
tuned-2.13.0-6.el8.noarch
4.18.0-192.rt13.50.el8.x86_64


How reproducible:
100%


Steps to Reproduce:
1. Uncomment "isolate_managed_irq=Y" in /etc/tuned/realtime-variables.conf, it doesn't work. Kernel option shows "isolcpus=X-Y", but we expect "isolcpus=managed_irq,domain,X-Y". 

cat /etc/tuned/realtime-variables.conf 
# Examples:
# isolated_cores=2,4-7
# isolated_cores=2-23
#
#
# Uncomment the 'isolate_managed_irq=Y' bellow if you want to move kernel
# managed IRQs out of isolated cores. Note that this requires kernel
# support. Please only specify this parameter if you are sure that the
# kernel supports it.
#
# isolate_managed_irq=Y


2. Specify "isolate_managed_irq=Y" in /etc/tuned/realtime-virtual-host-variables.conf, it works as expected in RT host.

# cat /etc/tuned/realtime-virtual-host-variables.conf 
isolated_cores=1,3,5,7,9,11,13,15,17,19,12,14,16,18
isolate_managed_irq=Y

# cat /proc/cmdline 
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-192.rt13.50.el8.x86_64 root=/dev/mapper/rhel_dell--per430--09-root ro crashkernel=auto resume=/dev/mapper/rhel_dell--per430--09-swap rd.lvm.lv=rhel_dell-per430-09/root rd.lvm.lv=rhel_dell-per430-09/swap console=ttyS0,115200n81 skew_tick=1 isolcpus=managed_irq,domain,1,3,5,7,9,11,13,15,17,19,12,14,16,18 intel_pstate=disable nosoftlockup nohz=on nohz_full=1,3,5,7,9,11,13,15,17,19,12,14,16,18 rcu_nocbs=1,3,5,7,9,11,13,15,17,19,12,14,16,18 default_hugepagesz=1G iommu=pt intel_iommu=on tsc=nowatchdog mitigations=off


3. Specify "isolate_managed_irq=Y" in /etc/tuned/realtime-virtual-guest-variables.conf, it works as expected in RT guest.

# cat /etc/tuned/realtime-virtual-guest-variables.conf 
isolated_cores=1
isolate_managed_irq=Y

# cat /proc/cmdline 
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-192.rt13.50.el8.x86_64 root=/dev/mapper/rhel_vm--73--232-root ro console=tty0 console=ttyS0,115200n8 biosdevname=0 crashkernel=auto resume=/dev/mapper/rhel_vm--73--232-swap rd.lvm.lv=rhel_vm-73-232/root rd.lvm.lv=rhel_vm-73-232/swap skew_tick=1 isolcpus=managed_irq,domain,1 intel_pstate=disable nosoftlockup nohz=on nohz_full=1 rcu_nocbs=1 default_hugepagesz=1G iommu=pt intel_iommu=on tsc=nowatchdog mitigations=off


Actual results:
"isolate_managed_irq=Y" doesn't be mentioned in "/etc/tuned/realtime-virtual-*-variables.conf".

Expected results:
"isolate_managed_irq=Y" should be mentioned in "/etc/tuned/realtime-virtual-*-variables.conf".


Additional info:
1. RHEL8.2 RT has "isolate_managed_irq=Y" after fix of Bug 1797025.
Comment 1 Pei Zhang 2020-03-27 04:00:08 UTC 
(In reply to Pei Zhang from comment #0)

...
> 
> 
> Steps to Reproduce:
> 1. Uncomment "isolate_managed_irq=Y" in /etc/tuned/realtime-variables.conf,
> it doesn't work. Kernel option shows "isolcpus=X-Y", but we expect
> "isolcpus=managed_irq,domain,X-Y". 

I was using: 

# tuned-adm profile realtime-virtual-host

# tuned-adm profile realtime-virtual-guest
Comment 3 Prasad Pandit 2021-06-02 11:47:11 UTC 
Raised PR#352 upstream
  -> https://github.com/redhat-performance/tuned/pull/352
Comment 4 Prasad Pandit 2021-06-07 07:29:14 UTC 
Merged upstream:
  -> https://github.com/redhat-performance/tuned/commit/f860e726b95eda3ce11d727e255a4e384566e058
Comment 10 errata-xmlrpc 2021-11-09 19:58:24 UTC 
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 (tuned bug fix and enhancement update), 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/RHBA-2021:4476
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