Bug 1957741

Summary:	[irqbalance] -i and -m options do not force irqbalance to avoid IRQ affinity changes
Product:	Red Hat Enterprise Linux 9	Reporter:	Adrian Tomasov <atomasov>
Component:	irqbalance	Assignee:	Kairui Song <kasong>
Status:	CLOSED NOTABUG	QA Contact:	Jiri Dluhos <jdluhos>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	9.0	CC:	aokuliar, atomasov, jeder, jhladky, jshortt, osabart, rvr
Target Milestone:	beta
Target Release:	---
Hardware:	Unspecified
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-06-04 08:09:51 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Adrian Tomasov 2021-05-06 11:38:20 UTC

Description of problem:
The current release of irqbalance does not allow us to manually specify IRQ affinity
using tuna for specific NIC/module. The IRQs are firstly banned using the -i parameter
followed by the tuna command for manual affinity changes. After a few seconds, the IRQ
affinity is changed by a background task (probably irqbalance). This behavior
causes a performance drop on an AMD Epyc system with 200 Gb NIC.

We also tried the -m parameter to ban all IRQs of a specific module, but the result is the 
same as -i parameter. 

Version-Release number of selected component (if applicable):
irqbalance-1.7.0-5.el9.x86_64

How reproducible:
always

Steps to Reproduce:
1. Install RHEL-9.0.0-20210420.2
2. Install irqbalance and tuna
3. systemctl enable irqbalance
4. reboot
5. for i in $(cat /proc/interrupts | grep mlx5 | cut -f1 -d:); do irqbalance -i $i; done
6. tuna --irqs mlx5*  --cpus 0-47 --spread
7. watch -n 0.2 tuna --irqs mlx5* -Q

Actual results:
Specific IRQs are distributed by irqbalance.

Expected results:
Specific IRQs are not distributed by irqbalance after IRQ affinity modification by tuna.

Additional info:

Comment 1 Adam Okuliar 2021-06-04 08:09:51 UTC

Sorry we misunderstood irqbalance manual page. Irqbalance command line options have to be passed via systemd at the boot time. 
Correct way to do this is via /usr/lib/irqbalance/defaults.env which is processed by systemd at the boot time.

IGNORED="mlx5_core"
ARGS=""
for i in $(cat /proc/interrupts | grep $IGNORED | cut -f1 -d:); do ARGS="$ARGS -i $i"; done
echo IRQBALANCE_ARGS=\"$ARGS\" > /usr/lib/irqbalance/defaults.env 

alternatively

IGNORED="mlx5"
echo IRQBALANCE_ARGS=\" -m $IGNORED\" > /usr/lib/irqbalance/defaults.env 

closing as NOTABUG.