dvfs agent 0.1

agent/main.go

@@ -0,0 +1,181 @@
+package main
+
+import (
+	"io"
+	"log/slog"
+	"math"
+	"net/http"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+type cpuHandler struct {
+	corePaths []string
+	maxFreq   int
+	minFreq   int
+	logger    *slog.Logger
+}
+
+// readIntFromFile reads the given file until the end
+// and converts the contained string into an integer
+func readIntFromFile(path string) (int, error) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.Atoi(strings.TrimSpace(string(b)))
+}
+
+func enumerateCPUCores(logger *slog.Logger) ([]string, int, int, error) {
+	files, err := os.ReadDir("/sys/devices/system/cpu/")
+	if err != nil {
+		logger.Error("reading /sys/devices/system/cpu/", "err", err)
+		return nil, -1, -1, err
+	}
+	r, _ := regexp.Compile("cpu([0-9]+)")
+
+	freqPaths := make([]string, 0)
+	maxF := math.MaxInt
+	minF := math.MinInt
+
+	// we look for cpuN directories
+	for _, f := range files {
+		if !f.IsDir() || !r.MatchString(f.Name()) {
+			continue
+		}
+
+		// read files for min & max freqs
+		dir := "/sys/devices/system/cpu/" + f.Name() + "/cpufreq/"
+		minFreq, err := readIntFromFile(dir + "cpuinfo_min_freq")
+		if err != nil {
+			logger.Error("failed to read cpu min freq", "path", dir+"cpuinfo_min_freq", "error", err)
+			continue
+		}
+		maxFreq, err := readIntFromFile(dir + "cpuinfo_max_freq")
+		if err != nil {
+			logger.Error("failed to read cpu max freq", "path", dir+"cpuinfo_min_freq", "error", err)
+			continue
+		}
+		freqPaths = append(freqPaths, dir+"scaling_max_freq")
+		maxF = min(maxF, maxFreq)
+		minF = max(minF, minFreq)
+	}
+	return freqPaths, minF, maxF, nil
+}
+
+func (s *cpuHandler) handleMin(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "GET" {
+		writeResponse("invalid method", http.StatusBadRequest, w, s.logger)
+		return
+	}
+	writeResponse(strconv.Itoa(s.minFreq), http.StatusOK, w, s.logger)
+}
+
+func (s *cpuHandler) handleMax(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "GET" {
+		writeResponse("invalid method", http.StatusBadRequest, w, s.logger)
+		return
+	}
+	writeResponse(strconv.Itoa(s.maxFreq), http.StatusOK, w, s.logger)
+}
+
+func (s *cpuHandler) handleCurrent(w http.ResponseWriter, r *http.Request) {
+	switch r.Method {
+	case "GET":
+		maxFreq := math.MinInt
+		for _, core := range s.corePaths {
+			freq, err := readIntFromFile(core)
+			if err != nil {
+				s.logger.Error("error while reading core frequency", "core", core, "error", err)
+				writeResponse("internal server error", http.StatusInternalServerError, w, s.logger)
+				return
+			}
+			s.logger.Debug("core frequency", "core", core, "frequency", freq)
+			maxFreq = max(maxFreq, freq)
+		}
+		s.logger.Debug("reported frequency", "freq", maxFreq)
+		writeResponse(strconv.Itoa(maxFreq), http.StatusOK, w, s.logger)
+	case "PUT":
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			s.logger.Error("failed to read the request body", "err", err)
+			writeResponse("internal server error", http.StatusInternalServerError, w, s.logger)
+		}
+		bodyStr := strings.TrimSpace(string(body))
+		// Check if it is an integer
+		freqInt, err := strconv.Atoi(bodyStr)
+		if err != nil {
+			s.logger.Error("failed to convert body to int", "error", err)
+			writeResponse("bad request", http.StatusBadRequest, w, s.logger)
+		}
+		if freqInt < s.minFreq || freqInt > s.maxFreq {
+			s.logger.Warn("requested frequency is out-of-bounds", "freq", freqInt, "min", s.minFreq, "max", s.maxFreq)
+			freqInt = max(s.minFreq, min(freqInt, s.maxFreq))
+			bodyStr = strconv.Itoa(freqInt)
+		}
+		s.logger.Info("requested to set current frequency", "frequency", bodyStr)
+		success := true
+		for _, core := range s.corePaths {
+			err = os.WriteFile(core, []byte(bodyStr), 0)
+			if err != nil {
+				s.logger.Error("failed to set core frequency", "core", core, "error", err)
+				success = false
+			}
+		}
+		if success {
+			w.WriteHeader(http.StatusOK)
+		} else {
+			w.WriteHeader(http.StatusInternalServerError)
+		}
+	default:
+		s.logger.Error("unexpected method for current cpu", "method", r.Method)
+		writeResponse("invalid method", http.StatusBadRequest, w, s.logger)
+	}
+}
+
+func (s *cpuHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	requestedPath := getStrippedRequestPath(r.URL, r.Pattern)
+	switch requestedPath {
+	case "frequency/min":
+		s.handleMin(w, r)
+		return
+	case "frequency/max":
+		s.handleMax(w, r)
+		return
+	case "frequency/current":
+		s.handleCurrent(w, r)
+		return
+	default:
+		s.logger.Error("unknown resource", "path", requestedPath)
+		writeResponse("not found", http.StatusNotFound, w, s.logger)
+	}
+}
+
+func main() {
+	appEnv := os.Getenv("AGENT_ENV")
+	loggerOpts := &slog.HandlerOptions{
+		Level: slog.LevelDebug,
+	}
+	var handler slog.Handler = slog.NewTextHandler(os.Stdout, loggerOpts)
+	if appEnv == "production" {
+		loggerOpts.Level = slog.LevelInfo
+		handler = slog.NewJSONHandler(os.Stdout, loggerOpts)
+	}
+	logger := slog.New(handler)
+
+	freqPaths, minF, maxF, err := enumerateCPUCores(logger)
+	if err != nil {
+		os.Exit(1)
+	}
+
+	cpuHandler := &cpuHandler{
+		logger:    logger,
+		maxFreq:   maxF,
+		minFreq:   minF,
+		corePaths: freqPaths,
+	}
+	http.Handle("/cpu/", logRequests(logger, cpuHandler))
+	logger.Info("exit", "result", http.ListenAndServe(":8080", nil))
+}