Check if cgroup cpu limits are defined to get the number of CPUs

internal/runtime/cpu.go

@@ -0,0 +1,64 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package runtime
+
+import (
+	"io/ioutil"
+	"math"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+
+	libcontainercgroups "github.com/opencontainers/runc/libcontainer/cgroups"
+)
+
+// NumCPU returns the number of logical CPUs usable by the current process.
+// If CPU cgroups limits are configured, use cfs_quota_us / cfs_period_us
+// as formula
+//  https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt
+func NumCPU() int {
+	cpus := runtime.NumCPU()
+
+	cgroupPath, err := libcontainercgroups.FindCgroupMountpoint("cpu")
+	if err != nil {
+		return cpus
+	}
+
+	cpuQuota := readCgroupFileToInt64(cgroupPath, "cpu.cfs_quota_us")
+	cpuPeriod := readCgroupFileToInt64(cgroupPath, "cpu.cfs_period_us")
+
+	if cpuQuota == -1 || cpuPeriod == -1 {
+		return cpus
+	}
+
+	return int(math.Ceil(float64(cpuQuota) / float64(cpuPeriod)))
+}
+
+func readCgroupFileToInt64(cgroupPath, cgroupFile string) int64 {
+	contents, err := ioutil.ReadFile(filepath.Join(cgroupPath, cgroupFile))
+	if err != nil {
+		return -1
+	}
+
+	strValue := strings.TrimSpace(string(contents))
+	if value, err := strconv.ParseInt(strValue, 10, 64); err == nil {
+		return value
+	}
+
+	return -1
+}