internal/plot: rewrite in a more declarative way (WIP)

Author: arl

internal/plot/layouts.go

@@ -397,6 +397,7 @@ var memoryClassesLayout = Scatter{
 <i>Profiling buckets</i> is <b>/memory/classes/profiling/buckets</b>, memory that is used by the stack trace hash map used for profiling.
 <i>Total</i> is <b>/memory/classes/total</b>, all memory mapped by the Go runtime into the current process as read-write.`,
 }
+
 var cpuClassesLayout = Scatter{
 	Name:   "TODO",
 	Title:  "CPU classes (GC)",

internal/plot/plots.go

@@ -56,7 +56,7 @@ func init() {
 				"/gc/heap/goal:bytes",
 			},
 			layout: heapDetailslLayout,
-			make:   makeHeapGlobal,
+			make:   makeHeapDetails,
 		},
 		{
 			name: "live-objects",
@@ -412,6 +412,11 @@ func makeGCPauses(indices ...int) runtimeMetric {
 }
 
 func (p *gcpauses) values(samples []metrics.Sample) any {
+	if p.histfactor == 0 {
+		gcpauses := samples[p.idxgcpauses].Value.Float64Histogram()
+		p.histfactor = downsampleFactor(len(gcpauses.Buckets), maxBuckets)
+	}
+
 	gcpauses := samples[p.idxgcpauses].Value.Float64Histogram()
 	return downsampleCounts(gcpauses, p.histfactor, p.counts[:])
 }
@@ -432,6 +437,11 @@ func makeRunnableTime(indices ...int) runtimeMetric {
 }
 
 func (p *runnableTime) values(samples []metrics.Sample) any {
+	if p.histfactor == 0 {
+		schedlat := samples[p.idxschedlat].Value.Float64Histogram()
+		p.histfactor = downsampleFactor(len(schedlat.Buckets), maxBuckets)
+	}
+
 	schedlat := samples[p.idxschedlat].Value.Float64Histogram()
 
 	return downsampleCounts(schedlat, p.histfactor, p.counts[:])

internal/plot/registry.go

@@ -77,19 +77,33 @@ func enabledPlots() []rtplot {
 		if plot.make == nil {
 			continue
 		}
+
 		indices, enabled := indicesFor(plot.metrics...)
 		if enabled {
 			plots = append(plots, rtplot{
 				name:   plot.name,
 				rt:     plot.make(indices...),
-				layout: plot.layout,
+				layout: assignName(plot.layout, plot.name),
 			})
 		}
 	}
 
 	return plots
 }
 
+func assignName(layout any, name string) any {
+	switch layout := layout.(type) {
+	case Scatter:
+		layout.Name = name
+		return layout
+	case Heatmap:
+		layout.Name = name
+		return layout
+	default:
+		panic(fmt.Sprintf("unknown plot layout type %T", layout))
+	}
+}
+
 func (pl *List) Config() *Config {
 	pl.once.Do(func() {
 		pl.rtPlots = enabledPlots()
@@ -168,8 +182,8 @@ func (pl *List) WriteValues(w io.Writer) error {
 	return nil
 }
 
-// mapMetricsToIndices retrieves indices for the specified metrics, returning
-// both the indices and whether all metrics were found.
+// indicesFor retrieves indices for the specified metrics, and a boolean
+// indicating whether they were all found.
 func indicesFor(metricNames ...string) ([]int, bool) {
 	indices := make([]int, len(metricNames))
 	allFound := true