Update the number of logical CPUs dynamically in system plugin (#6214)

plugins/inputs/system/README.md

@@ -3,6 +3,8 @@
 The system plugin gathers general stats on system load, uptime,
 and number of users logged in. It is similar to the unix `uptime` command.
 
+Number of CPUs is obtained from the /proc/cpuinfo file.
+
 ### Configuration:
 
 ```toml

plugins/inputs/system/system.go

@@ -6,12 +6,12 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"runtime"
 	"strings"
 	"time"
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
+	"github.com/shirou/gopsutil/cpu"
 	"github.com/shirou/gopsutil/host"
 	"github.com/shirou/gopsutil/load"
 )
@@ -35,11 +35,16 @@ func (_ *SystemStats) Gather(acc telegraf.Accumulator) error {
 		return err
 	}
 
+	numCPUs, err := cpu.Counts(true)
+	if err != nil {
+		return err
+	}
+
 	fields := map[string]interface{}{
 		"load1":  loadavg.Load1,
 		"load5":  loadavg.Load5,
 		"load15": loadavg.Load15,
-		"n_cpus": runtime.NumCPU(),
+		"n_cpus": numCPUs,
 	}
 
 	users, err := host.Users()