Remove -cpu flag (#2793)

The -cpu flag is a weird one (and copied originally from Caddy), it
basically sets GOMAXPROCS which can be *easily* done by just setting
that environment variable. Also with systemd and containerized env you
set this externally *anyway*, so there is little use to do this again in
the binary.

Also the option's help was confusing (i.e. percentage of what?). Remove
the option and supporting files.
Signed-off-by: Miek Gieben <miek@miek.nl>

coredns.1.md

@@ -24,9 +24,6 @@ Available options:
 : specify Corefile to load, if not given CoreDNS will look for a `Corefile` in the current
   directory.
 
-**-cpu** **CAP**
-: specify maximum CPU capacity in percent.
-
 **-dns.port** **PORT**
 : override default port (53) to listen on.
 

coremain/run.go

@@ -2,14 +2,12 @@
 package coremain
 
 import (
-	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
 	"os"
 	"runtime"
-	"strconv"
 	"strings"
 
 	"github.com/coredns/coredns/core/dnsserver"
@@ -24,7 +22,6 @@ func init() {
 	setVersion()
 
 	flag.StringVar(&conf, "conf", "", "Corefile to load (default \""+caddy.DefaultConfigFile+"\")")
-	flag.StringVar(&cpu, "cpu", "100%", "CPU cap")
 	flag.BoolVar(&plugins, "plugins", false, "List installed plugins")
 	flag.StringVar(&caddy.PidFile, "pidfile", "", "Path to write pid file")
 	flag.BoolVar(&version, "version", false, "Show version")
@@ -73,11 +70,6 @@ func Run() {
 		os.Exit(0)
 	}
 
-	// Set CPU cap
-	if err := setCPU(cpu); err != nil {
-		mustLogFatal(err)
-	}
-
 	// Get Corefile input
 	corefile, err := caddy.LoadCaddyfile(serverType)
 	if err != nil {
@@ -194,45 +186,9 @@ func setVersion() {
 	}
 }
 
-// setCPU parses string cpu and sets GOMAXPROCS
-// according to its value. It accepts either
-// a number (e.g. 3) or a percent (e.g. 50%).
-func setCPU(cpu string) error {
-	var numCPU int
-
-	availCPU := runtime.NumCPU()
-
-	if strings.HasSuffix(cpu, "%") {
-		// Percent
-		var percent float32
-		pctStr := cpu[:len(cpu)-1]
-		pctInt, err := strconv.Atoi(pctStr)
-		if err != nil || pctInt < 1 || pctInt > 100 {
-			return errors.New("invalid CPU value: percentage must be between 1-100")
-		}
-		percent = float32(pctInt) / 100
-		numCPU = int(float32(availCPU) * percent)
-	} else {
-		// Number
-		num, err := strconv.Atoi(cpu)
-		if err != nil || num < 1 {
-			return errors.New("invalid CPU value: provide a number or percent greater than 0")
-		}
-		numCPU = num
-	}
-
-	if numCPU > availCPU {
-		numCPU = availCPU
-	}
-
-	runtime.GOMAXPROCS(numCPU)
-	return nil
-}
-
 // Flags that control program flow or startup
 var (
 	conf    string
-	cpu     string
 	logfile bool
 	version bool
 	plugins bool

coremain/run_test.go

-package coremain
-
-import (
-	"runtime"
-	"testing"
-)
-
-func TestSetCPU(t *testing.T) {
-	currentCPU := runtime.GOMAXPROCS(-1)
-	maxCPU := runtime.NumCPU()
-	halfCPU := int(0.5 * float32(maxCPU))
-	if halfCPU < 1 {
-		halfCPU = 1
-	}
-	for i, test := range []struct {
-		input     string
-		output    int
-		shouldErr bool
-	}{
-		{"1", 1, false},
-		{"-1", currentCPU, true},
-		{"0", currentCPU, true},
-		{"100%", maxCPU, false},
-		{"50%", halfCPU, false},
-		{"110%", currentCPU, true},
-		{"-10%", currentCPU, true},
-		{"invalid input", currentCPU, true},
-		{"invalid input%", currentCPU, true},
-		{"9999", maxCPU, false}, // over available CPU
-	} {
-		err := setCPU(test.input)
-		if test.shouldErr && err == nil {
-			t.Errorf("Test %d: Expected error, but there wasn't any", i)
-		}
-		if !test.shouldErr && err != nil {
-			t.Errorf("Test %d: Expected no error, but there was one: %v", i, err)
-		}
-		if actual, expected := runtime.GOMAXPROCS(-1), test.output; actual != expected {
-			t.Errorf("Test %d: GOMAXPROCS was %d but expected %d", i, actual, expected)
-		}
-		// teardown
-		runtime.GOMAXPROCS(currentCPU)
-	}
-}