fix #51135 make CFS quota period configurable, adds a cli flag and config option to kubelet to be able to set cpu.cfs_period and defaults to 100ms as before.

It requires to enable feature gate CustomCPUCFSQuotaPeriod.

Signed-off-by: Sandor Szücs <sandor.szuecs@zalando.de>

pkg/kubelet/kuberuntime/helpers_linux.go

@@ -18,6 +18,11 @@ limitations under the License.
 
 package kuberuntime
 
+import (
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	kubefeatures "k8s.io/kubernetes/pkg/features"
+)
+
 const (
 	// Taken from lmctfy https://github.com/google/lmctfy/blob/master/lmctfy/controllers/cpu_controller.cc
 	minShares     = 2
@@ -25,7 +30,7 @@ const (
 	milliCPUToCPU = 1000
 
 	// 100000 is equivalent to 100ms
-	quotaPeriod    = 100 * minQuotaPeriod
+	quotaPeriod    = 100000
 	minQuotaPeriod = 1000
 )
 
@@ -44,21 +49,22 @@ func milliCPUToShares(milliCPU int64) int64 {
 }
 
 // milliCPUToQuota converts milliCPU to CFS quota and period values
-func milliCPUToQuota(milliCPU int64) (quota int64, period int64) {
+func milliCPUToQuota(milliCPU int64, period int64) (quota int64) {
 	// CFS quota is measured in two values:
 	//  - cfs_period_us=100ms (the amount of time to measure usage across)
 	//  - cfs_quota=20ms (the amount of cpu time allowed to be used across a period)
 	// so in the above example, you are limited to 20% of a single CPU
 	// for multi-cpu environments, you just scale equivalent amounts
+	// see https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt for details
 	if milliCPU == 0 {
 		return
 	}
-
-	// we set the period to 100ms by default
-	period = quotaPeriod
+	if !utilfeature.DefaultFeatureGate.Enabled(kubefeatures.CPUCFSQuotaPeriod) {
+		period = quotaPeriod
+	}
 
 	// we then convert your milliCPU to a value normalized over a period
-	quota = (milliCPU * quotaPeriod) / milliCPUToCPU
+	quota = (milliCPU * period) / milliCPUToCPU
 
 	// quota needs to be a minimum of 1ms.
 	if quota < minQuotaPeriod {