fix for overview panel

internal/hoststats/cpu_unix.go

@@ -0,0 +1,79 @@
+//go:build !windows
+
+package hoststats
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// cpuSampler computes CPU busy% from successive cumulative /proc/stat
+// snapshots. The kernel's counters are monotonic totals since boot, so a
+// single read can't give a percentage -- only the delta between two reads
+// separated by real time can. sampleOnce (its only caller) already runs on
+// a fixed poll interval, so that interval doubles as the sampling window;
+// no internal sleep needed.
+type cpuSampler struct {
+	prevTotal uint64
+	prevIdle  uint64
+	have      bool
+}
+
+func (c *cpuSampler) sample() float64 {
+	total, idle, err := readProcStatCPU()
+	if err != nil {
+		return 0
+	}
+	if !c.have {
+		c.prevTotal, c.prevIdle = total, idle
+		c.have = true
+		return 0
+	}
+	deltaTotal := total - c.prevTotal
+	deltaIdle := idle - c.prevIdle
+	c.prevTotal, c.prevIdle = total, idle
+	if deltaTotal == 0 {
+		return 0
+	}
+	pct := (1 - float64(deltaIdle)/float64(deltaTotal)) * 100
+	switch {
+	case pct < 0:
+		pct = 0
+	case pct > 100:
+		pct = 100
+	}
+	return pct
+}
+
+// readProcStatCPU parses the aggregate "cpu " line: user nice system idle
+// iowait irq softirq steal guest guest_nice (guest/guest_nice already
+// double-counted inside user/nice on Linux, per `man proc`, so they're not
+// added again here). idle = idle + iowait, matching the convention `top`
+// and most load calculators use.
+func readProcStatCPU() (total, idle uint64, err error) {
+	data, err := os.ReadFile("/proc/stat")
+	if err != nil {
+		return 0, 0, err
+	}
+	line, _, _ := strings.Cut(string(data), "\n")
+	fields := strings.Fields(line)
+	if len(fields) < 5 || fields[0] != "cpu" {
+		return 0, 0, fmt.Errorf("hoststats: unexpected /proc/stat format")
+	}
+	values := make([]uint64, 0, len(fields)-1)
+	for _, f := range fields[1:] {
+		v, err := strconv.ParseUint(f, 10, 64)
+		if err != nil {
+			return 0, 0, err
+		}
+		values = append(values, v)
+		total += v
+	}
+	idle = values[3]
+	if len(values) > 4 {
+		idle += values[4] // iowait
+	}
+	return total, idle, nil
+}