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Add systemd-less mode for Libvirt collector #377

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Merged
merged 3 commits into from
Jul 16, 2025
Merged

Add systemd-less mode for Libvirt collector #377

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a73e1df
added non-systemd cgroup mode
wtripp180901 Jul 4, 2025
d623547
fixes and formatting
wtripp180901 Jul 4, 2025
7e84cb7
autodetect cgroup layout + tweaks
wtripp180901 Jul 15, 2025
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44 changes: 36 additions & 8 deletions pkg/collector/cgroup.go
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,11 @@ const (
netSubsystem = "net_cls,net_prio"
)

const (
systemdSlicesName = "machine.slice"
nonSystemdSlicesName = "machine"
)

// Regular expressions of cgroup paths for different resource managers.
// ^.*/(?:(.*?)_)?slurm(?:_(.*?)/)?(?:.*?)/job_([0-9]+)(?:.*$)
// ^.*/slurm(?:_(.*?))?/(?:.*?)/job_([0-9]+)(?:.*$)
Expand All @@ -98,9 +103,12 @@ var (

For v2 possibilities are /machine.slice/machine-qemu\x2d2\x2dinstance\x2d00000001.scope
/machine.slice/machine-qemu\x2d2\x2dinstance\x2d00000001.scope/libvirt

Non systemd: machine/qemu-1-instance1.libvirt-qemu
*/
var (
libvirtCgroupPathRegex = regexp.MustCompile("^.*/(?:.+?)-qemu-(?:[0-9]+)-(?P<id>instance-[0-9a-f]+)(?:.*$)")
libvirtCgroupPathRegex = regexp.MustCompile("^.*/(?:.+?)-qemu-(?:[0-9]+)-(?P<id>instance-[0-9a-f]+)(?:.*$)")
libvirtCgroupNoSystemdPathRegex = regexp.MustCompile("^.*/(?:.+?)qemu-(?:[0-9]+)-(?P<id>instance-[0-9a-f]+)(?:.*$)")
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I think a regex regexp.MustCompile("^.*/(?:.+?)qemu-(?:[0-9]+)-(?P<id>instance-[0-9a-f]+)(?:.*$)") must work for both cases. So, I think there is no need to define two?!

)

// Ref: https://linuxera.org/cpu-memory-management-kubernetes-cgroupsv2/
Expand Down Expand Up @@ -137,8 +145,29 @@ var (
"collector.cgroups.force-version",
"Set cgroups version manually. Used only for testing.",
).Hidden().Enum("v1", "v2")

noSystemdMode = CEEMSExporterApp.Flag(
"collector.cgroups.no-systemd-mode",
"Set if running on a non-systemd host",
).Default("false").Bool()
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Instead of using a CLI flag (which users have to configure), we should be able to detect the cgroup layout, right?! This is what we are doing for k8s to detect if we are using cgroupfs or systemd drivers. We can use a similar logic here as well. We can add a field to cgroupManager something like nonSystemdLayout bool and set it to true when machine is found. Something like:

// Discover all cgroup layout
for _, slice := range []string{"machine", "machine.slice"} {
	if _, err := os.Stat(filepath.Join(*cgroupfsPath, activeSubsystem, slice)); err == nil {
		manager.slices = append(manager.slices, slice)
                if slice == "machine" {
                   manager.nonSystemdLayout = true
                }
                break // This should be fine as there will atmost one of machine or machine.slice exist at any given time
	}
}

Eventually we can use the manager.nonSysytemdLayout when parsing number of vCPUs. What do you think?

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yeah that sounds sensible

)

func resolveSlices(nonSystemdMode bool) string {
if nonSystemdMode {
return nonSystemdSlicesName
} else {
return systemdSlicesName
}
}

func resolveLibvirtRegex(nonSystemdMode bool) *regexp.Regexp {
if nonSystemdMode {
return libvirtCgroupNoSystemdPathRegex
} else {
return libvirtCgroupPathRegex
}
}

// resolveSubsystem returns the resolved cgroups v1 subsystem.
func resolveSubsystem(subsystem string) string {
switch subsystem {
Expand Down Expand Up @@ -311,7 +340,7 @@ func NewCgroupManager(name manager, logger *slog.Logger) (*cgroupManager, error)
fs: fs,
mode: cgroups.Unified,
root: *cgroupfsPath,
slices: []string{"machine.slice"},
slices: []string{resolveSlices(*noSystemdMode)},
}
} else {
var mode cgroups.CGMode
Expand All @@ -330,7 +359,7 @@ func NewCgroupManager(name manager, logger *slog.Logger) (*cgroupManager, error)
mode: mode,
root: *cgroupfsPath,
activeController: activeSubsystem,
slices: []string{"machine.slice"},
slices: []string{resolveSlices(*noSystemdMode)},
}
}

Expand All @@ -339,10 +368,10 @@ func NewCgroupManager(name manager, logger *slog.Logger) (*cgroupManager, error)
manager.name = rmNames[name]

// Add path regex
manager.idRegex = libvirtCgroupPathRegex
manager.idRegex = resolveLibvirtRegex(*noSystemdMode)

// Identify child cgroup
// In cgroups v1, all the child cgroups like emulator, vcpu* are flat whereas
// In cgroups v1 or on a non-systemd host, all the child cgroups like emulator, vcpu* are flat whereas
// in v2 they are all inside libvirt child
manager.isChild = func(p string) bool {
return strings.Contains(p, "/libvirt") || strings.Contains(p, "/emulator") || strings.Contains(p, "/vcpu")
Expand Down Expand Up @@ -1078,10 +1107,9 @@ func (c *cgroupCollector) cpusFromChildren(path string) (int, error) {
// In cgroup v1, they are flat whereas in cgroup v2 they are inside libvirt folder
var vcpuPath string

switch c.cgroupManager.mode { //nolint:exhaustive
case cgroups.Unified:
if c.cgroupManager.mode == cgroups.Unified && !(*noSystemdMode) {
vcpuPath = fmt.Sprintf("%s%s/libvirt/vcpu*", c.cgroupManager.root, path)
default:
} else {
vcpuPath = fmt.Sprintf("%s%s/vcpu*", c.cgroupManager.root, path)
}

Expand Down