feat(tools/scheddomain): add a tool to report on scheduler domains

Change-Id: Ia4e1aa1e7fc48b8bfb619aba9ba71037ffcc69f8
Reviewed-on: https://cl.fcuny.net/c/world/+/451
Tested-by: CI
Reviewed-by: Franck Cuny <franck@fcuny.net>

2 files changed, 156 insertions, 0 deletions

diff --git a/tools/scheddomain/go.mod b/tools/scheddomain/go.mod
new file mode 100644
index 0000000..afbc83a
--- /dev/null
+++ b/tools/scheddomain/go.mod
@@ -0,0 +1,3 @@
+module golang.fcuny.net/scheddomain
+
+go 1.17
diff --git a/tools/scheddomain/main.go b/tools/scheddomain/main.go
new file mode 100644
index 0000000..1d0f5d3
--- /dev/null
+++ b/tools/scheddomain/main.go
@@ -0,0 +1,153 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/+/v4.17/include/linux/sched/topology.h#20
+var SDFlags = map[string]uint64{
+	"SD_LOAD_BALANCE":        0x0001,
+	"SD_BALANCE_NEWIDLE":     0x0002,
+	"SD_BALANCE_EXEC":        0x0004,
+	"SD_BALANCE_FORK":        0x0008,
+	"SD_BALANCE_WAKE":        0x0010,
+	"SD_WAKE_AFFINE":         0x0020,
+	"SD_ASYM_CPUCAPACITY":    0x0040,
+	"SD_SHARE_CPUCAPACITY":   0x0080,
+	"SD_SHARE_POWERDOMAIN":   0x0100,
+	"SD_SHARE_PKG_RESOURCES": 0x0200,
+	"SD_SERIALIZE":           0x0400,
+	"SD_ASYM_PACKING":        0x0800,
+	"SD_PREFER_SIBLING":      0x1000,
+	"SD_OVERLAP":             0x2000,
+	"SD_NUMA":                0x4000,
+}
+
+type Scheduler map[string][]Domain
+
+type Domain struct {
+	Name    string            `json:"name"`
+	Type    string            `json:"type"`
+	Flags   []string          `json:"flags"`
+	Indexes map[string]string `json:"indexes"`
+}
+
+func main() {
+	cpus, err := CPUs()
+	if err != nil {
+		fmt.Fprint(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	if len(cpus) == 0 {
+		fmt.Fprint(os.Stderr, "there is no scheduler domains\n")
+		os.Exit(1)
+	}
+
+	sched := Scheduler{}
+	for _, cpu := range cpus {
+		_, cpuID := path.Split(cpu)
+		domains, err := domains(cpu)
+		if err != nil {
+			fmt.Fprint(os.Stderr, err)
+			os.Exit(1)
+		}
+		sched[cpuID] = domains
+	}
+	out, err := json.Marshal(sched)
+	if err != nil {
+		fmt.Fprint(os.Stderr, err)
+		os.Exit(1)
+	}
+	fmt.Println(string(out))
+}
+
+func domains(cpuPath string) ([]Domain, error) {
+	domainPath := fmt.Sprintf("%s/domain*", cpuPath)
+	availDomains, err := filepath.Glob(domainPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get domains under %s: %v", cpuPath, err)
+	}
+
+	domains := []Domain{}
+
+	if len(availDomains) == 0 {
+		return domains, nil
+	}
+
+	for _, d := range availDomains {
+		_, dName := path.Split(d)
+		dType := getContent(d, "name")
+		flags, err := domainFlags(d)
+		if err != nil {
+			return nil, err
+		}
+		indexes := domainIndexes(d)
+
+		domain := Domain{
+			Name:    dName,
+			Type:    dType,
+			Flags:   flags,
+			Indexes: indexes,
+		}
+		domains = append(domains, domain)
+	}
+	return domains, nil
+}
+
+func domainFlags(path string) ([]string, error) {
+	flagPath := fmt.Sprintf("%s/flags", path)
+
+	content, err := ioutil.ReadFile(flagPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read %s: %v", flagPath, err)
+	}
+
+	flags, err := strconv.ParseUint(strings.TrimSpace(string(content)), 0, 64)
+	if err != nil {
+		return nil, fmt.Errorf("failed to convert flags %s: %v", flagPath, err)
+	}
+
+	supportedFlags := []string{}
+	for k, v := range SDFlags {
+		if flags&v > 0 {
+			supportedFlags = append(supportedFlags, k)
+		}
+	}
+	return supportedFlags, nil
+}
+
+func domainIndexes(path string) map[string]string {
+	indexes := map[string]string{
+		"busy":      getContent(path, "busy_idx"),
+		"idle":      getContent(path, "idle_idx"),
+		"new_idle":  getContent(path, "newidle_idx"),
+		"wake":      getContent(path, "wake_idx"),
+		"fork_exec": getContent(path, "forkexec_idx"),
+	}
+	return indexes
+}
+
+func getContent(path, fileName string) string {
+	domainName := fmt.Sprintf("%s/%s", path, fileName)
+	name, err := ioutil.ReadFile(domainName)
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(name))
+}
+
+func CPUs() ([]string, error) {
+	cpus, err := filepath.Glob("/proc/sys/kernel/sched_domain/cpu*")
+	if err != nil {
+		return nil, fmt.Errorf("failed to get a list of cpus: %v", err)
+	}
+	return cpus, nil
+}