tun: Drop the staged timing metrics

flow.go

@@ -1,13 +1,10 @@
 package nebula
 
 import (
-	"fmt"
 	"log/slog"
 	"runtime"
 	"sync"
-	"time"
 
-	"github.com/rcrowley/go-metrics"
 	"github.com/slackhq/nebula/config"
 	"github.com/slackhq/nebula/noiseutil"
 )
@@ -25,10 +22,6 @@ import (
 // Metrics are registered only for active pipelines. flow.{tx,rx}.batches counts reads handed to the ordered stage and
 // flow.{tx,rx}.inline those the reader handled itself (TX inline also counts oversized reads); their rates show
 // whether staging is used. flow.tx.gate_switches counts transmit switches between inline and fanout mode.
-// flow.stage.<stage>.q<queue>.busy_ns locates the limiting stage: tx_read, tx_encrypt, tx_send, rx_read, rx_decrypt or
-// rx_write. Take rates; 1e9 ns/s fills a serial stage. These are elapsed times that exclude read syscalls and
-// downstream waits; descheduling inflates them and worker times add up across the pool.
-// Inline work counts at the reader; small RX batches sent to the writer include decryption in writer time.
 
 // stagedConfig is tun.staged. workers is per routine and direction; zero keeps processing inline.
 type stagedConfig struct {
@@ -112,38 +105,17 @@ type flowPool struct {
 	wg   sync.WaitGroup
 }
 
-func newFlowPool(workers, queueLen int, busy metrics.Counter) *flowPool {
+func newFlowPool(workers, queueLen int) *flowPool {
 	p := &flowPool{jobs: make(chan flowJob, queueLen)}
 	for range workers {
 		p.wg.Go(func() {
 			nb := make([]byte, 12)
 			for job := range p.jobs {
-				// One pair of clock reads covers a run of jobs that are queued back to back
-				t := time.Now()
-				for job != nil {
-					job.run(nb)
-					job = p.next()
-				}
-				busy.Inc(int64(time.Since(t)))
+				job.run(nb)
 			}
 		})
 	}
 	return p
 }
 
-// next returns the next queued job without waiting, or nil.
-func (p *flowPool) next() flowJob {
-	select {
-	case job := <-p.jobs:
-		return job
-	default:
-		return nil
-	}
-}
-
 func (p *flowPool) close() { close(p.jobs); p.wg.Wait() }
-
-// stageBusy is the busy time counter of one stage of routine q.
-func stageBusy(stage string, q int) metrics.Counter {
-	return metrics.GetOrRegisterCounter(fmt.Sprintf("flow.stage.%s.q%d.busy_ns", stage, q), nil)
-}