Bug 2170290

Summary:	IODeviceWeight= just ignored
Product:	Red Hat Enterprise Linux 9	Reporter:	Kazuo Moriwaka <kmoriwak>
Component:	systemd	Assignee:	systemd-maint
Status:	CLOSED CURRENTRELEASE	QA Contact:	Frantisek Sumsal <fsumsal>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	9.1	CC:	dtardon, systemd-maint-list
Target Milestone:	rc	Keywords:	Bugfix, Reproducer, TestOnly, Triaged
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2023-02-16 09:23:33 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:
Bug Depends On:	2138081
Bug Blocks:

Description Kazuo Moriwaka 2023-02-16 03:06:45 UTC

Description of problem:

In a systemd service unit, IODeviceWeight= settings have no effect.

Version-Release number of selected component (if applicable):

systemd-250-12.el9_1.1

How reproducible:

Always

Steps to Reproduce:
1. systemctl set-property chronyd.service IODeviceWeight="/dev/sda 95" 
2. cat /sys/fs/cgroup/system.slice/chronyd.service/io.bfq.weight


Actual results:

default 100

Expected results:

default 100
8:0 95

Additional info:

There are two options to set the I/O weight for a specific block device; io.bfq.weight provided by kernel and io.weight supported by systemd.
Setting the io.weight for a specific block device is unsupported because RHEL9 kernel doesn't set kernel option BLK_CGROUP_IOCOST.

# cat /boot/config-<ver> |grep "BLK_CGROUP_IOCOST"
# CONFIG_BLK_IOCOST is not set

systemd v250 doesn't support per-device IO weight with io.bfq.weight.

And systemd v251 support io.bfq.weight
https://github.com/systemd/systemd/commit/9f0c0c4e158e835c7227dd677d6148607eece89d