Estimate fan duty from observed RPM maxima

audit/internal/platform/benchmark.go

@@ -1122,6 +1122,7 @@ type benchmarkCoolingSample struct {
 	AvgFanRPM             float64
 	AvgFanDutyCyclePct    float64
 	FanDutyCycleAvailable bool
+	FanDutyCycleEstimated bool
 }
 
 func sampleBenchmarkTelemetry(gpuIndices []int) ([]GPUMetricRow, error) {
@@ -1134,6 +1135,7 @@ func sampleBenchmarkTelemetry(gpuIndices []int) ([]GPUMetricRow, error) {
 		samples[i].FanAvgRPM = fanSample.AvgFanRPM
 		samples[i].FanDutyCyclePct = fanSample.AvgFanDutyCyclePct
 		samples[i].FanDutyCycleAvailable = fanSample.FanDutyCycleAvailable
+		samples[i].FanDutyCycleEstimated = fanSample.FanDutyCycleEstimated
 	}
 	return samples, nil
 }
@@ -1141,11 +1143,12 @@ func sampleBenchmarkTelemetry(gpuIndices []int) ([]GPUMetricRow, error) {
 func sampleBenchmarkCoolingSample() benchmarkCoolingSample {
 	fans, _ := sampleFanSpeeds()
 	avgRPM, _, _ := fanRPMStats(fans)
-	dutyPct, dutyAvailable := sampleFanDutyCyclePct()
+	dutyPct, dutyAvailable, dutyEstimated := sampleFanDutyCyclePctFromFans(fans)
 	return benchmarkCoolingSample{
 		AvgFanRPM:             avgRPM,
 		AvgFanDutyCyclePct:    dutyPct,
 		FanDutyCycleAvailable: dutyAvailable,
+		FanDutyCycleEstimated: dutyEstimated,
 	}
 }
 
@@ -1387,25 +1390,33 @@ func summarizeBenchmarkCooling(rows []GPUMetricRow) *BenchmarkCoolingSummary {
 	}
 	var rpmValues []float64
 	var dutyValues []float64
+	var dutyEstimated bool
 	for _, row := range rows {
 		if row.FanAvgRPM > 0 {
 			rpmValues = append(rpmValues, row.FanAvgRPM)
 		}
 		if row.FanDutyCycleAvailable {
 			dutyValues = append(dutyValues, row.FanDutyCyclePct)
+			if row.FanDutyCycleEstimated {
+				dutyEstimated = true
+			}
 		}
 	}
 	if len(rpmValues) == 0 && len(dutyValues) == 0 {
 		return nil
 	}
 	summary := &BenchmarkCoolingSummary{
-		Available: true,
-		AvgFanRPM: benchmarkMean(rpmValues),
+		Available:             true,
+		AvgFanRPM:             benchmarkMean(rpmValues),
+		FanDutyCycleEstimated: dutyEstimated,
 	}
 	if len(dutyValues) > 0 {
 		summary.FanDutyCycleAvailable = true
 		summary.AvgFanDutyCyclePct = benchmarkMean(dutyValues)
 		summary.P95FanDutyCyclePct = benchmarkPercentile(dutyValues, 95)
+		if summary.FanDutyCycleEstimated {
+			summary.Notes = append(summary.Notes, "fan duty cycle is estimated from the highest fan RPM observed since boot; treat it as an approximation, not a direct PWM reading")
+		}
 	} else {
 		summary.Notes = append(summary.Notes, "fan duty cycle unavailable on this host; RPM-only fan telemetry was collected")
 	}

audit/internal/platform/benchmark_types.go

@@ -31,6 +31,7 @@ type BenchmarkCoolingSummary struct {
 	Available             bool     `json:"available"`
 	AvgFanRPM             float64  `json:"avg_fan_rpm,omitempty"`
 	FanDutyCycleAvailable bool     `json:"fan_duty_cycle_available,omitempty"`
+	FanDutyCycleEstimated bool     `json:"fan_duty_cycle_estimated,omitempty"`
 	AvgFanDutyCyclePct    float64  `json:"avg_fan_duty_cycle_pct,omitempty"`
 	P95FanDutyCyclePct    float64  `json:"p95_fan_duty_cycle_pct,omitempty"`
 	Notes                 []string `json:"notes,omitempty"`
@@ -55,32 +56,32 @@ type NvidiaBenchmarkOptions struct {
 }
 
 type NvidiaBenchmarkResult struct {
-	BenchmarkVersion   string                       `json:"benchmark_version"`
-	GeneratedAt        time.Time                    `json:"generated_at"`
-	Hostname           string                       `json:"hostname,omitempty"`
-	ServerModel        string                       `json:"server_model,omitempty"`
-	BenchmarkProfile   string                       `json:"benchmark_profile"`
-	ParallelGPUs       bool                         `json:"parallel_gpus,omitempty"`
-	RampStep           int                          `json:"ramp_step,omitempty"`
-	RampTotal          int                          `json:"ramp_total,omitempty"`
-	RampRunID          string                       `json:"ramp_run_id,omitempty"`
-	ScalabilityScore   float64                      `json:"scalability_score,omitempty"`
+	BenchmarkVersion string    `json:"benchmark_version"`
+	GeneratedAt      time.Time `json:"generated_at"`
+	Hostname         string    `json:"hostname,omitempty"`
+	ServerModel      string    `json:"server_model,omitempty"`
+	BenchmarkProfile string    `json:"benchmark_profile"`
+	ParallelGPUs     bool      `json:"parallel_gpus,omitempty"`
+	RampStep         int       `json:"ramp_step,omitempty"`
+	RampTotal        int       `json:"ramp_total,omitempty"`
+	RampRunID        string    `json:"ramp_run_id,omitempty"`
+	ScalabilityScore float64   `json:"scalability_score,omitempty"`
 	// PlatformPowerScore is the mean compute scalability across ramp steps 2..N.
 	// 100% = each added GPU contributes exactly its single-card throughput.
 	// < 100% = throughput loss due to thermal throttle, power limits, or contention.
-	PlatformPowerScore   float64                    `json:"platform_power_score,omitempty"`
-	PerformanceRampSteps []NvidiaPerformanceRampStep `json:"performance_ramp_steps,omitempty"`
-	OverallStatus      string                       `json:"overall_status"`
-	SelectedGPUIndices []int                        `json:"selected_gpu_indices"`
-	Findings           []string                     `json:"findings,omitempty"`
-	Warnings           []string                     `json:"warnings,omitempty"`
-	Normalization      BenchmarkNormalization       `json:"normalization"`
-	HostConfig         *BenchmarkHostConfig         `json:"host_config,omitempty"`
-	CPULoad            *BenchmarkCPULoad            `json:"cpu_load,omitempty"`
-	Cooling            *BenchmarkCoolingSummary     `json:"cooling,omitempty"`
-	GPUs               []BenchmarkGPUResult         `json:"gpus"`
-	Interconnect       *BenchmarkInterconnectResult `json:"interconnect,omitempty"`
-	ServerPower        *BenchmarkServerPower        `json:"server_power,omitempty"`
+	PlatformPowerScore   float64                      `json:"platform_power_score,omitempty"`
+	PerformanceRampSteps []NvidiaPerformanceRampStep  `json:"performance_ramp_steps,omitempty"`
+	OverallStatus        string                       `json:"overall_status"`
+	SelectedGPUIndices   []int                        `json:"selected_gpu_indices"`
+	Findings             []string                     `json:"findings,omitempty"`
+	Warnings             []string                     `json:"warnings,omitempty"`
+	Normalization        BenchmarkNormalization       `json:"normalization"`
+	HostConfig           *BenchmarkHostConfig         `json:"host_config,omitempty"`
+	CPULoad              *BenchmarkCPULoad            `json:"cpu_load,omitempty"`
+	Cooling              *BenchmarkCoolingSummary     `json:"cooling,omitempty"`
+	GPUs                 []BenchmarkGPUResult         `json:"gpus"`
+	Interconnect         *BenchmarkInterconnectResult `json:"interconnect,omitempty"`
+	ServerPower          *BenchmarkServerPower        `json:"server_power,omitempty"`
 }
 
 type BenchmarkNormalization struct {
@@ -223,8 +224,8 @@ type BenchmarkScorecard struct {
 
 	// Throttle breakdown — percentage of steady-state time in each throttle type.
 	// Used for diagnosis: tells WHY the GPU throttled, not just whether it did.
-	ThermalThrottlePct  float64 `json:"thermal_throttle_pct"`  // HW+SW thermal slowdown
-	PowerCapThrottlePct float64 `json:"power_cap_throttle_pct"` // SW power cap
+	ThermalThrottlePct   float64 `json:"thermal_throttle_pct"`   // HW+SW thermal slowdown
+	PowerCapThrottlePct  float64 `json:"power_cap_throttle_pct"` // SW power cap
 	SyncBoostThrottlePct float64 `json:"sync_boost_throttle_pct,omitempty"`
 
 	// Temperature headroom: distance to the 100°C destruction threshold.
@@ -300,22 +301,22 @@ type NvidiaPowerBenchResult struct {
 	// PlatformMaxTDPW is the sum of per-GPU stable power limits found during the
 	// cumulative thermal ramp. Represents the actual sustained power budget of
 	// this server under full GPU load. Use for rack power planning.
-	PlatformMaxTDPW float64               `json:"platform_max_tdp_w"`
+	PlatformMaxTDPW float64 `json:"platform_max_tdp_w"`
 	// ServerPower captures IPMI server power delta (idle→loaded) measured in
 	// parallel with the thermal ramp. Use to compare GPU-reported TDP against
 	// actual wall-power draw as seen by the server's power supply.
-	ServerPower     *BenchmarkServerPower `json:"server_power,omitempty"`
-	Findings        []string              `json:"findings,omitempty"`
-	GPUs            []NvidiaPowerBenchGPU `json:"gpus"`
+	ServerPower *BenchmarkServerPower `json:"server_power,omitempty"`
+	Findings    []string              `json:"findings,omitempty"`
+	GPUs        []NvidiaPowerBenchGPU `json:"gpus"`
 }
 
 type NvidiaPowerBenchGPU struct {
-	Index               int      `json:"index"`
-	Name                string   `json:"name,omitempty"`
-	BusID               string   `json:"bus_id,omitempty"`
-	DefaultPowerLimitW  float64  `json:"default_power_limit_w,omitempty"`
+	Index              int     `json:"index"`
+	Name               string  `json:"name,omitempty"`
+	BusID              string  `json:"bus_id,omitempty"`
+	DefaultPowerLimitW float64 `json:"default_power_limit_w,omitempty"`
 	// AppliedPowerLimitW is the stable limit found during single-card calibration.
-	AppliedPowerLimitW  float64  `json:"applied_power_limit_w,omitempty"`
+	AppliedPowerLimitW float64 `json:"applied_power_limit_w,omitempty"`
 	// StablePowerLimitW is the final fixed limit for this GPU after the
 	// cumulative thermal ramp. This is the limit at which the GPU operated
 	// stably with all other GPUs running simultaneously at their own limits.
@@ -333,10 +334,10 @@ type NvidiaPowerBenchGPU struct {
 }
 
 type NvidiaPowerBenchStep struct {
-	StepIndex           int      `json:"step_index"`
-	GPUIndices          []int    `json:"gpu_indices"`
+	StepIndex  int   `json:"step_index"`
+	GPUIndices []int `json:"gpu_indices"`
 	// NewGPUIndex is the GPU whose stable limit was searched in this step.
-	NewGPUIndex         int      `json:"new_gpu_index"`
+	NewGPUIndex int `json:"new_gpu_index"`
 	// NewGPUStableLimitW is the stable power limit found for the new GPU.
 	NewGPUStableLimitW  float64  `json:"new_gpu_stable_limit_w,omitempty"`
 	TotalObservedPowerW float64  `json:"total_observed_power_w,omitempty"`
@@ -349,15 +350,15 @@ type NvidiaPowerBenchStep struct {
 // NvidiaPerformanceRampStep holds per-step performance data for the
 // scalability ramp-up phase of the performance benchmark.
 type NvidiaPerformanceRampStep struct {
-	StepIndex          int      `json:"step_index"`
-	GPUIndices         []int    `json:"gpu_indices"`
+	StepIndex  int   `json:"step_index"`
+	GPUIndices []int `json:"gpu_indices"`
 	// TotalSyntheticTOPS is the sum of per-GPU SyntheticScore (fp32-equivalent
 	// TOPS from dedicated single-precision phases) across all GPUs in this step.
-	TotalSyntheticTOPS float64  `json:"total_synthetic_tops"`
-	TotalMixedTOPS     float64  `json:"total_mixed_tops,omitempty"`
+	TotalSyntheticTOPS float64 `json:"total_synthetic_tops"`
+	TotalMixedTOPS     float64 `json:"total_mixed_tops,omitempty"`
 	// ScalabilityPct = TotalSyntheticTOPS / (k × best_single_gpu_tops) × 100.
 	// 100% = perfect linear scaling. < 100% = thermal/power/interconnect loss.
-	ScalabilityPct     float64  `json:"scalability_pct"`
-	Status             string   `json:"status"`
-	Notes              []string `json:"notes,omitempty"`
+	ScalabilityPct float64  `json:"scalability_pct"`
+	Status         string   `json:"status"`
+	Notes          []string `json:"notes,omitempty"`
 }

audit/internal/platform/gpu_metrics.go

@@ -27,6 +27,7 @@ type GPUMetricRow struct {
 	FanAvgRPM             float64 `json:"fan_avg_rpm,omitempty"`
 	FanDutyCyclePct       float64 `json:"fan_duty_cycle_pct,omitempty"`
 	FanDutyCycleAvailable bool    `json:"fan_duty_cycle_available,omitempty"`
+	FanDutyCycleEstimated bool    `json:"fan_duty_cycle_estimated,omitempty"`
 }
 
 // sampleGPUMetrics runs nvidia-smi once and returns current metrics for each GPU.
@@ -147,14 +148,18 @@ func sampleAMDGPUMetrics() ([]GPUMetricRow, error) {
 // WriteGPUMetricsCSV writes collected rows as a CSV file.
 func WriteGPUMetricsCSV(path string, rows []GPUMetricRow) error {
 	var b bytes.Buffer
-	b.WriteString("stage,elapsed_sec,gpu_index,temperature_c,usage_pct,mem_usage_pct,power_w,clock_mhz,mem_clock_mhz,fan_avg_rpm,fan_duty_cycle_pct,fan_duty_cycle_available\n")
+	b.WriteString("stage,elapsed_sec,gpu_index,temperature_c,usage_pct,mem_usage_pct,power_w,clock_mhz,mem_clock_mhz,fan_avg_rpm,fan_duty_cycle_pct,fan_duty_cycle_available,fan_duty_cycle_estimated\n")
 	for _, r := range rows {
 		dutyAvail := 0
 		if r.FanDutyCycleAvailable {
 			dutyAvail = 1
 		}
-		fmt.Fprintf(&b, "%s,%.1f,%d,%.1f,%.1f,%.1f,%.1f,%.0f,%.0f,%.0f,%.1f,%d\n",
-			strconv.Quote(strings.TrimSpace(r.Stage)), r.ElapsedSec, r.GPUIndex, r.TempC, r.UsagePct, r.MemUsagePct, r.PowerW, r.ClockMHz, r.MemClockMHz, r.FanAvgRPM, r.FanDutyCyclePct, dutyAvail)
+		dutyEstimated := 0
+		if r.FanDutyCycleEstimated {
+			dutyEstimated = 1
+		}
+		fmt.Fprintf(&b, "%s,%.1f,%d,%.1f,%.1f,%.1f,%.1f,%.0f,%.0f,%.0f,%.1f,%d,%d\n",
+			strconv.Quote(strings.TrimSpace(r.Stage)), r.ElapsedSec, r.GPUIndex, r.TempC, r.UsagePct, r.MemUsagePct, r.PowerW, r.ClockMHz, r.MemClockMHz, r.FanAvgRPM, r.FanDutyCyclePct, dutyAvail, dutyEstimated)
 	}
 	return os.WriteFile(path, b.Bytes(), 0644)
 }

audit/internal/platform/sat_fan_stress.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"math"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -56,13 +57,37 @@ type cachedPowerReading struct {
 	UpdatedAt time.Time
 }
 
+type fanObservationState struct {
+	MaxRPM map[string]float64 `json:"max_rpm"`
+}
+
+type fanPeakCandidate struct {
+	FirstSeen time.Time
+	RPM       float64
+}
+
 var (
 	systemPowerCacheMu sync.Mutex
 	systemPowerCache   cachedPowerReading
+	fanObservationMu   sync.Mutex
+	fanObservation     fanObservationState
+	fanObservationInit bool
+	fanPeakCandidates  = make(map[string]fanPeakCandidate)
 )
 
 const systemPowerHoldTTL = 15 * time.Second
 
+var fanObservationStatePath = "/var/log/bee-sat/fan-observation.json"
+
+const fanObservationMinPeakHold = time.Second
+
+func normalizeObservedFanMaxRPM(rpm float64) float64 {
+	if rpm <= 0 {
+		return 0
+	}
+	return math.Ceil(rpm/1000.0) * 1000.0
+}
+
 // RunFanStressTest runs a two-phase GPU stress test while monitoring fan speeds,
 // temperatures, and power draw every second. Exports metrics.csv and fan-sensors.csv.
 // Designed to reproduce case-04 fan-speed lag and detect GPU thermal throttling.
@@ -310,11 +335,13 @@ func sampleFanSpeeds() ([]FanReading, error) {
 	out, err := exec.Command("ipmitool", "sdr", "type", "Fan").Output()
 	if err == nil {
 		if fans := parseFanSpeeds(string(out)); len(fans) > 0 {
+			updateFanObservation(fans, time.Now())
 			return fans, nil
 		}
 	}
 	fans, sensorsErr := sampleFanSpeedsViaSensorsJSON()
 	if len(fans) > 0 {
+		updateFanObservation(fans, time.Now())
 		return fans, nil
 	}
 	if err != nil {
@@ -323,6 +350,119 @@ func sampleFanSpeeds() ([]FanReading, error) {
 	return nil, sensorsErr
 }
 
+func loadFanObservationLocked() {
+	if fanObservationInit {
+		return
+	}
+	fanObservationInit = true
+	fanObservation.MaxRPM = make(map[string]float64)
+	raw, err := os.ReadFile(fanObservationStatePath)
+	if err != nil || len(raw) == 0 {
+		return
+	}
+	var persisted fanObservationState
+	if json.Unmarshal(raw, &persisted) != nil {
+		return
+	}
+	for name, rpm := range persisted.MaxRPM {
+		name = strings.TrimSpace(name)
+		if name == "" || rpm <= 0 {
+			continue
+		}
+		fanObservation.MaxRPM[name] = rpm
+	}
+}
+
+func saveFanObservationLocked() {
+	if len(fanObservation.MaxRPM) == 0 {
+		return
+	}
+	dir := filepath.Dir(fanObservationStatePath)
+	if dir == "" || dir == "." {
+		dir = "/var/log/bee-sat"
+	}
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return
+	}
+	raw, err := json.MarshalIndent(fanObservation, "", "  ")
+	if err != nil {
+		return
+	}
+	_ = os.WriteFile(fanObservationStatePath, raw, 0644)
+}
+
+func updateFanObservation(fans []FanReading, now time.Time) {
+	if len(fans) == 0 {
+		return
+	}
+	fanObservationMu.Lock()
+	defer fanObservationMu.Unlock()
+	loadFanObservationLocked()
+	changed := false
+	for _, fan := range fans {
+		name := strings.TrimSpace(fan.Name)
+		if name == "" || fan.RPM <= 0 {
+			continue
+		}
+		currentMax := fanObservation.MaxRPM[name]
+		if fan.RPM <= currentMax {
+			delete(fanPeakCandidates, name)
+			continue
+		}
+		if cand, ok := fanPeakCandidates[name]; ok {
+			if now.Sub(cand.FirstSeen) >= fanObservationMinPeakHold {
+				newMax := math.Max(cand.RPM, fan.RPM)
+				if newMax > currentMax {
+					fanObservation.MaxRPM[name] = normalizeObservedFanMaxRPM(newMax)
+					changed = true
+				}
+				delete(fanPeakCandidates, name)
+				continue
+			}
+			if fan.RPM > cand.RPM {
+				fanPeakCandidates[name] = fanPeakCandidate{FirstSeen: cand.FirstSeen, RPM: fan.RPM}
+			}
+			continue
+		}
+		fanPeakCandidates[name] = fanPeakCandidate{FirstSeen: now, RPM: fan.RPM}
+	}
+	if changed {
+		saveFanObservationLocked()
+	}
+}
+
+func estimateFanDutyCyclePctFromObservation(fans []FanReading) (float64, bool) {
+	if len(fans) == 0 {
+		return 0, false
+	}
+	fanObservationMu.Lock()
+	defer fanObservationMu.Unlock()
+	loadFanObservationLocked()
+	var samples []float64
+	for _, fan := range fans {
+		name := strings.TrimSpace(fan.Name)
+		if name == "" || fan.RPM <= 0 {
+			continue
+		}
+		maxRPM := fanObservation.MaxRPM[name]
+		if maxRPM <= 0 {
+			continue
+		}
+		pct := fan.RPM / maxRPM * 100.0
+		if pct > 100 {
+			pct = 100
+		}
+		if pct < 0 {
+			pct = 0
+		}
+		samples = append(samples, pct)
+	}
+	if len(samples) == 0 {
+		return 0, false
+	}
+	return benchmarkMean(samples), true
+}
+
 // parseFanSpeeds parses "ipmitool sdr type Fan" output.
 // Handles two formats:
 //
@@ -428,12 +568,27 @@ func sampleFanSpeedsViaSensorsJSON() ([]FanReading, error) {
 
 // sampleFanDutyCyclePct reads fan PWM/duty-cycle controls from lm-sensors.
 // Returns the average duty cycle across all exposed PWM controls.
-func sampleFanDutyCyclePct() (float64, bool) {
+func sampleFanDutyCyclePct() (float64, bool, bool) {
 	out, err := exec.Command("sensors", "-j").Output()
 	if err != nil || len(out) == 0 {
-		return 0, false
+		fans, fanErr := sampleFanSpeeds()
+		if fanErr != nil {
+			return 0, false, false
+		}
+		return sampleFanDutyCyclePctFromFans(fans)
 	}
-	return parseFanDutyCyclePctSensorsJSON(out)
+	pct, ok := parseFanDutyCyclePctSensorsJSON(out)
+	return pct, ok, false
+}
+
+func sampleFanDutyCyclePctFromFans(fans []FanReading) (float64, bool, bool) {
+	if len(fans) == 0 {
+		return 0, false, false
+	}
+	if pct, ok := estimateFanDutyCyclePctFromObservation(fans); ok {
+		return pct, true, true
+	}
+	return 0, false, false
 }
 
 func parseFanDutyCyclePctSensorsJSON(raw []byte) (float64, bool) {

audit/internal/platform/sat_fan_stress_test.go

@@ -1,6 +1,7 @@
 package platform
 
 import (
+	"path/filepath"
 	"testing"
 	"time"
 )
@@ -50,6 +51,53 @@ func TestParseFanDutyCyclePctSensorsJSON(t *testing.T) {
 	}
 }
 
+func TestEstimateFanDutyCyclePctFromObservation(t *testing.T) {
+	t.Parallel()
+
+	oldPath := fanObservationStatePath
+	oldState := fanObservation
+	oldInit := fanObservationInit
+	oldCandidates := fanPeakCandidates
+	fanObservationStatePath = filepath.Join(t.TempDir(), "fan-observation.json")
+	fanObservation = fanObservationState{}
+	fanObservationInit = false
+	fanPeakCandidates = make(map[string]fanPeakCandidate)
+	t.Cleanup(func() {
+		fanObservationStatePath = oldPath
+		fanObservation = oldState
+		fanObservationInit = oldInit
+		fanPeakCandidates = oldCandidates
+	})
+
+	start := time.Unix(100, 0)
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5000}}, start)
+	if _, ok := estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2500}}); ok {
+		t.Fatalf("single-sample spike should not establish observed max")
+	}
+
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5200}}, start.Add(500*time.Millisecond))
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5100}}, start.Add(1500*time.Millisecond))
+
+	got, ok := estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2600}})
+	if !ok {
+		t.Fatalf("expected estimated duty cycle from persisted observed max")
+	}
+	if got < 43 || got > 44 {
+		t.Fatalf("got=%v want ~43.3", got)
+	}
+
+	fanObservation = fanObservationState{}
+	fanObservationInit = false
+	fanPeakCandidates = make(map[string]fanPeakCandidate)
+	got, ok = estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2600}})
+	if !ok {
+		t.Fatalf("expected persisted observed max to be reloaded from disk")
+	}
+	if got < 43 || got > 44 {
+		t.Fatalf("reloaded got=%v want ~43.3", got)
+	}
+}
+
 func TestParseDCMIPowerReading(t *testing.T) {
 	raw := `
 Instantaneous power reading:                   512 Watts