@@ -3468,6 +3468,10 @@ paths:

         The `precpu_stats` is the CPU statistic of last read, which is used

         for calculating the CPU usage percentage. It is not the same as the

         `cpu_stats` field.

+

+        If either `precpu_stats.online_cpus` or `cpu_stats.online_cpus` is

+        nil then for compatibility with older daemons the length of the

+        corresponding `cpu_usage.percpu_usage` array should be used.

       operationId: "ContainerStats"

       produces: ["application/json"]

       responses:

@@ -3546,6 +3550,7 @@ paths:

                   total_usage: 100215355

                   usage_in_kernelmode: 30000000

                 system_cpu_usage: 739306590000000

+                online_cpus: 4

                 throttling_data:

                   periods: 0

                   throttled_periods: 0

@@ -3561,6 +3566,7 @@ paths:

                   total_usage: 100093996

                   usage_in_kernelmode: 30000000

                 system_cpu_usage: 9492140000000

+                online_cpus: 4

                 throttling_data:

                   periods: 0

                   throttled_periods: 0

@@ -47,6 +47,9 @@ type CPUStats struct {

 	// System Usage. Linux only.

 	SystemUsage uint64 `json:"system_cpu_usage,omitempty"`

+	// Online CPUs. Linux only.

+	OnlineCPUs uint32 `json:"online_cpus,omitempty"`

+

 	// Throttling Data. Linux only.

 	ThrottlingData ThrottlingData `json:"throttling_data,omitempty"`

 }

@@ -178,10 +178,14 @@ func calculateCPUPercentUnix(previousCPU, previousSystem uint64, v *types.StatsJ

 		cpuDelta = float64(v.CPUStats.CPUUsage.TotalUsage) - float64(previousCPU)

 		// calculate the change for the entire system between readings

 		systemDelta = float64(v.CPUStats.SystemUsage) - float64(previousSystem)

+		onlineCPUs  = float64(v.CPUStats.OnlineCPUs)

 	)

+	if onlineCPUs == 0.0 {

+		onlineCPUs = float64(len(v.CPUStats.CPUUsage.PercpuUsage))

+	}

 	if systemDelta > 0.0 && cpuDelta > 0.0 {

-		cpuPercent = (cpuDelta / systemDelta) * float64(len(v.CPUStats.CPUUsage.PercpuUsage)) * 100.0

+		cpuPercent = (cpuDelta / systemDelta) * onlineCPUs * 100.0

 	}

 	return cpuPercent

 }

@@ -80,6 +80,12 @@ func (s *Collector) Run() {

 			continue

 		}

+		onlineCPUs, err := s.getNumberOnlineCPUs()

+		if err != nil {

+			logrus.Errorf("collecting system online cpu count: %v", err)

+			continue

+		}

+

 		for _, pair := range pairs {

 			stats, err := s.supervisor.GetContainerStats(pair.container)

 			if err != nil {

@@ -97,6 +103,7 @@ func (s *Collector) Run() {

 			}

 			// FIXME: move to containerd on Linux (not Windows)

 			stats.CPUStats.SystemUsage = systemUsage

+			stats.CPUStats.OnlineCPUs = onlineCPUs

 			pair.publisher.Publish(*stats)

 		}

@@ -11,6 +11,11 @@ import (

 	"github.com/opencontainers/runc/libcontainer/system"

 )

+/*

+#include <unistd.h>

+*/

+import "C"

+

 // platformNewStatsCollector performs platform specific initialisation of the

 // Collector structure.

 func platformNewStatsCollector(s *Collector) {

@@ -64,3 +69,11 @@ func (s *Collector) getSystemCPUUsage() (uint64, error) {

 	}

 	return 0, fmt.Errorf("invalid stat format. Error trying to parse the '/proc/stat' file")

 }

+

+func (s *Collector) getNumberOnlineCPUs() (uint32, error) {

+	i, err := C.sysconf(C._SC_NPROCESSORS_ONLN)

+	if err != nil {

+		return 0, err

+	}

+	return uint32(i), nil

+}

@@ -13,3 +13,7 @@ func platformNewStatsCollector(s *Collector) {

 func (s *Collector) getSystemCPUUsage() (uint64, error) {

 	return 0, nil

 }

+

+func (s *Collector) getNumberOnlineCPUs() (uint32, error) {

+	return 0, nil

+}

@@ -24,6 +24,7 @@ keywords: "API, Docker, rcli, REST, documentation"

 * `POST /build` now accepts `extrahosts` parameter to specify a host to ip mapping to use during the build.

 * `POST /services/create` and `POST /services/(id or name)/update` now accept a `rollback` value for `FailureAction`.

 * `POST /services/create` and `POST /services/(id or name)/update` now accept an optional `RollbackConfig` object which specifies rollback options.

+* `GET /containers/(id or name)/stats` now includes an `online_cpus` field in both `precpu_stats` and `cpu_stats`. If this field is `nil` then for compatibility with older daemons the length of the corresponding `cpu_usage.percpu_usage` array should be used.

 ## v1.26 API changes