driver: set cpuset when using cgroups v2

This PR makes it so that the Podman driver will now respect the task
config resources.cores value. When set, the task will be assigned the
specified number of CPU cores to be allowed to run on.

Note: unlike the docker/exec drivers, podman tasks will not be also allowed
to make use of the "shared" set of cpu cores (ones that have not yet been
reserved specifically for a task). Most likely that feature will be removed
in the near future (~Nomad 1.7) anyway.

README.md

@@ -18,6 +18,7 @@ this plugin to Nomad!
 * Monitor the memory consumption
 * Monitor CPU usage
 * Task config cpu value is used to populate podman CpuShares
+* Task config cores value is used to populate podman Cpuset
 * Container log is forwarded to [Nomad logger](https://www.nomadproject.io/docs/commands/alloc/logs.html)
 * Utilize podmans --init feature
 * Set username or UID used for the specified command within the container (podman --user option).

driver.go

@@ -525,7 +525,7 @@ func (d *Driver) StartTask(cfg *drivers.TaskConfig) (*drivers.TaskHandle, *drive
 	}
 
 	// Set the nomad slice as cgroup parent
-	d.setupCgroup(createOpts)
+	d.setupCgroup(&createOpts)
 
 	// Resources config options
 	createOpts.ContainerResourceConfig.ResourceLimits = &spec.LinuxResources{
@@ -769,7 +769,7 @@ func (d *Driver) StartTask(cfg *drivers.TaskConfig) (*drivers.TaskHandle, *drive
 }
 
 // setupCgroup customizes where the cgroup lives (v2 only)
-func (d *Driver) setupCgroup(opts api.SpecGenerator) {
+func (d *Driver) setupCgroup(opts *api.SpecGenerator) {
 	if d.cgroupV2 {
 		opts.ContainerCgroupConfig.CgroupParent = "nomad.slice"
 	}
@@ -804,6 +804,11 @@ func memoryLimits(r drivers.MemoryResources, reservation string) (hard, soft *in
 }
 
 func setCPUResources(cfg TaskConfig, systemResources *drivers.LinuxResources, taskCPU *spec.LinuxCPU) error {
+	// always assign cpuset
+	taskCPU.Cpus = systemResources.CpusetCpus
+
+	// only set bandwidth if hard limit is enabled
+	// currently only docker and podman drivers provide this ability
 	if !cfg.CPUHardLimit {
 		return nil
 	}

driver_test.go

@@ -2123,6 +2123,28 @@ func createInspectImage(t *testing.T, image, reference string) {
 	must.Eq(t, idRef, idTest)
 }
 
+func Test_setTaskCpuset(t *testing.T) {
+	ci.Parallel(t)
+
+	t.Run("empty", func(t *testing.T) {
+		sysResources := &drivers.LinuxResources{CpusetCpus: ""}
+		taskCPU := new(spec.LinuxCPU)
+		cfg := TaskConfig{}
+		err := setCPUResources(cfg, sysResources, taskCPU)
+		must.NoError(t, err)
+		must.Eq(t, "", taskCPU.Cpus)
+	})
+
+	t.Run("non-empty", func(t *testing.T) {
+		sysResources := &drivers.LinuxResources{CpusetCpus: "2,5-8"}
+		taskCPU := new(spec.LinuxCPU)
+		cfg := TaskConfig{}
+		err := setCPUResources(cfg, sysResources, taskCPU)
+		must.NoError(t, err)
+		must.Eq(t, "2,5-8", taskCPU.Cpus)
+	})
+}
+
 func Test_cpuLimits(t *testing.T) {
 	ci.Parallel(t)