pkg/build: introduce the build jobs parameter

This parameter defines the number of cores dedicated to the kernel build
process. By default, it's equal to the number of available CPUs.

6 files changed, 26 insertions, 21 deletions

diff --git a/pkg/build/build.go b/pkg/build/build.go
index 4d6e3bce3..2274ceb8e 100644
--- a/pkg/build/build.go
+++ b/pkg/build/build.go
@@ -12,6 +12,7 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 	"time"
 
@@ -37,6 +38,7 @@ type Params struct {
 	SysctlFile   string
 	Config       []byte
 	Tracer       debugtracer.DebugTracer
+	BuildJobs    int // If 0, all CPUs will be used.
 	Build        json.RawMessage
 }
 
@@ -71,6 +73,9 @@ func Image(params Params) (details ImageDetails, err error) {
 	if params.Tracer == nil {
 		params.Tracer = &debugtracer.NullTracer{}
 	}
+	if params.BuildJobs == 0 {
+		params.BuildJobs = runtime.NumCPU()
+	}
 	var builder builder
 	builder, err = getBuilder(params.TargetOS, params.TargetArch, params.VMType)
 	if err != nil {
diff --git a/pkg/build/freebsd.go b/pkg/build/freebsd.go
index 2f4aa1313..2c6e0fcc9 100644
--- a/pkg/build/freebsd.go
+++ b/pkg/build/freebsd.go
@@ -45,12 +45,12 @@ options 	DIAGNOSTIC
 		return ImageDetails{}, err
 	}
 	objPrefix := filepath.Join(params.KernelDir, "obj")
-	output, err := ctx.make(params.KernelDir, objPrefix, "kernel-toolchain")
+	output, err := ctx.make(params.KernelDir, objPrefix, params.BuildJobs, "kernel-toolchain")
 	if err != nil {
 		return ImageDetails{}, err
 	}
-	if _, err := ctx.make(params.KernelDir, objPrefix, "buildkernel", "WITH_EXTRA_TCP_STACKS=",
-		fmt.Sprintf("KERNCONF=%v", confFile)); err != nil {
+	if _, err := ctx.make(params.KernelDir, objPrefix, params.BuildJobs, "buildkernel",
+		"WITH_EXTRA_TCP_STACKS=", fmt.Sprintf("KERNCONF=%v", confFile)); err != nil {
 		// The kernel-toolchain make target has to be built separately
 		// because FreeBSD's build doesn't correctly order the two
 		// targets. Its output is useful for debugging though, so
@@ -121,16 +121,16 @@ sudo mdconfig -d -u ${md#md}
 
 func (ctx freebsd) clean(kernelDir, targetArch string) error {
 	objPrefix := filepath.Join(kernelDir, "obj")
-	_, err := ctx.make(kernelDir, objPrefix, "cleanworld")
+	_, err := ctx.make(kernelDir, objPrefix, runtime.NumCPU(), "cleanworld")
 	return err
 }
 
-func (ctx freebsd) make(kernelDir, objPrefix string, makeArgs ...string) ([]byte, error) {
+func (ctx freebsd) make(kernelDir, objPrefix string, jobs int, makeArgs ...string) ([]byte, error) {
 	args := append([]string{
 		fmt.Sprintf("MAKEOBJDIRPREFIX=%v", objPrefix),
 		"make",
 		"-C", kernelDir,
-		"-j", strconv.Itoa(runtime.NumCPU()),
+		"-j", strconv.Itoa(jobs),
 	}, makeArgs...)
 	output, err := osutil.RunCmd(3*time.Hour, kernelDir, "sh", "-c", strings.Join(args, " "))
 	return output, err
diff --git a/pkg/build/linux.go b/pkg/build/linux.go
index 4069e0202..b68a87bc1 100644
--- a/pkg/build/linux.go
+++ b/pkg/build/linux.go
@@ -142,7 +142,7 @@ func (linux) createImage(params Params, kernelPath string) error {
 }
 
 func (linux) clean(kernelDir, targetArch string) error {
-	return runMakeImpl(targetArch, "", "", "", kernelDir, []string{"distclean"})
+	return runMakeImpl(targetArch, "", "", "", kernelDir, runtime.NumCPU(), []string{"distclean"})
 }
 
 func (linux) writeFile(file string, data []byte) error {
@@ -152,9 +152,9 @@ func (linux) writeFile(file string, data []byte) error {
 	return osutil.SandboxChown(file)
 }
 
-func runMakeImpl(arch, compiler, linker, ccache, kernelDir string, extraArgs []string) error {
+func runMakeImpl(arch, compiler, linker, ccache, kernelDir string, jobs int, extraArgs []string) error {
 	target := targets.Get(targets.Linux, arch)
-	args := LinuxMakeArgs(target, compiler, linker, ccache, "")
+	args := LinuxMakeArgs(target, compiler, linker, ccache, "", jobs)
 	args = append(args, extraArgs...)
 	cmd := osutil.Command("make", args...)
 	if err := osutil.Sandbox(cmd, true, true); err != nil {
@@ -179,12 +179,13 @@ func runMakeImpl(arch, compiler, linker, ccache, kernelDir string, extraArgs []s
 }
 
 func runMake(params Params, extraArgs ...string) error {
-	return runMakeImpl(params.TargetArch, params.Compiler, params.Linker, params.Ccache, params.KernelDir, extraArgs)
+	return runMakeImpl(params.TargetArch, params.Compiler, params.Linker, params.Ccache,
+		params.KernelDir, params.BuildJobs, extraArgs)
 }
 
-func LinuxMakeArgs(target *targets.Target, compiler, linker, ccache, buildDir string) []string {
+func LinuxMakeArgs(target *targets.Target, compiler, linker, ccache, buildDir string, jobs int) []string {
 	args := []string{
-		"-j", fmt.Sprint(runtime.NumCPU()),
+		"-j", fmt.Sprint(jobs),
 		"ARCH=" + target.KernelArch,
 	}
 	if target.Triple != "" {
diff --git a/pkg/build/netbsd.go b/pkg/build/netbsd.go
index 962b6e82c..80ea02481 100644
--- a/pkg/build/netbsd.go
+++ b/pkg/build/netbsd.go
@@ -44,25 +44,25 @@ func (ctx netbsd) build(params Params) (ImageDetails, error) {
 	if strings.HasSuffix(params.Compiler, "clang++") {
 		// Build tools before building kernel.
 		if _, err := osutil.RunCmd(60*time.Minute, params.KernelDir, "./build.sh", "-m", params.TargetArch,
-			"-U", "-j"+strconv.Itoa(runtime.NumCPU()), "-V", "MKCTF=no",
+			"-U", "-j"+strconv.Itoa(params.BuildJobs), "-V", "MKCTF=no",
 			"-V", "MKLLVM=yes", "-V", "MKGCC=no", "-V", "HAVE_LLVM=yes", "tools"); err != nil {
 			return ImageDetails{}, err
 		}
 
 		// Build kernel.
 		if _, err := osutil.RunCmd(20*time.Minute, params.KernelDir, "./build.sh", "-m", params.TargetArch,
-			"-U", "-j"+strconv.Itoa(runtime.NumCPU()), "-V", "MKCTF=no",
+			"-U", "-j"+strconv.Itoa(params.BuildJobs), "-V", "MKCTF=no",
 			"-V", "MKLLVM=yes", "-V", "MKGCC=no", "-V", "HAVE_LLVM=yes", "kernel="+kernelName); err != nil {
 			return ImageDetails{}, err
 		}
 	} else if strings.HasSuffix(params.Compiler, "g++") {
 		if _, err := osutil.RunCmd(30*time.Minute, params.KernelDir, "./build.sh", "-m", params.TargetArch,
-			"-U", "-j"+strconv.Itoa(runtime.NumCPU()), "-V", "MKCTF=no", "tools"); err != nil {
+			"-U", "-j"+strconv.Itoa(params.BuildJobs), "-V", "MKCTF=no", "tools"); err != nil {
 			return ImageDetails{}, err
 		}
 
 		if _, err := osutil.RunCmd(20*time.Minute, params.KernelDir, "./build.sh", "-m", params.TargetArch,
-			"-U", "-j"+strconv.Itoa(runtime.NumCPU()), "-V", "MKCTF=no", "kernel="+kernelName); err != nil {
+			"-U", "-j"+strconv.Itoa(params.BuildJobs), "-V", "MKCTF=no", "kernel="+kernelName); err != nil {
 			return ImageDetails{}, err
 		}
 	}
diff --git a/pkg/build/openbsd.go b/pkg/build/openbsd.go
index 97f7c6a8f..bb069f90b 100644
--- a/pkg/build/openbsd.go
+++ b/pkg/build/openbsd.go
@@ -6,7 +6,6 @@ package build
 import (
 	"fmt"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"time"
 
@@ -32,7 +31,7 @@ func (ctx openbsd) build(params Params) (ImageDetails, error) {
 		return ImageDetails{}, err
 	}
 	for _, tgt := range []string{"clean", "obj", "config", "all"} {
-		if err := ctx.make(compileDir, tgt); err != nil {
+		if err := ctx.make(compileDir, params.BuildJobs, tgt); err != nil {
 			return ImageDetails{}, err
 		}
 	}
@@ -63,8 +62,8 @@ func (ctx openbsd) clean(kernelDir, targetArch string) error {
 	return nil
 }
 
-func (ctx openbsd) make(kernelDir string, args ...string) error {
-	args = append([]string{"-j", strconv.Itoa(runtime.NumCPU())}, args...)
+func (ctx openbsd) make(kernelDir string, jobs int, args ...string) error {
+	args = append([]string{"-j", strconv.Itoa(jobs)}, args...)
 	_, err := osutil.RunCmd(10*time.Minute, kernelDir, "make", args...)
 	return err
 }
diff --git a/sys/syz-extract/linux.go b/sys/syz-extract/linux.go
index d30529ba9..b458122ad 100644
--- a/sys/syz-extract/linux.go
+++ b/sys/syz-extract/linux.go
@@ -79,7 +79,7 @@ func (*linux) prepareArch(arch *Arch) error {
 		return nil
 	}
 	kernelDir := arch.sourceDir
-	makeArgs := build.LinuxMakeArgs(arch.target, "", "", "", arch.buildDir)
+	makeArgs := build.LinuxMakeArgs(arch.target, "", "", "", arch.buildDir, runtime.NumCPU())
 	if arch.configFile != "" {
 		err := osutil.CopyFile(arch.configFile, filepath.Join(arch.buildDir, ".config"))
 		if err != nil {