add a metrics gauge for built block slot

vms/proposervm/batched_vm.go

@@ -145,6 +145,7 @@ func (vm *VM) BatchedParseBlock(ctx context.Context, blks [][]byte) ([]snowman.B
 					vm:       vm,
 					innerBlk: innerBlks[innerBlocksIndex],
 					status:   status,
+					slot:     unspecifiedSlotIndex,
 				},
 			}
 		} else {
@@ -154,6 +155,7 @@ func (vm *VM) BatchedParseBlock(ctx context.Context, blks [][]byte) ([]snowman.B
 					vm:       vm,
 					innerBlk: innerBlks[innerBlocksIndex],
 					status:   status,
+					slot:     unspecifiedSlotIndex,
 				},
 			}
 		}

vms/proposervm/block.go

@@ -24,6 +24,11 @@ import (
 const (
 	// allowable block issuance in the future
 	maxSkew = 10 * time.Second
+
+	// unspecifiedSlotIndex defines the default value being used for a proposal slot index, prior of being populated
+	// by the actual slot index. Given that the slot index is zero base, we would want to use an "invalid" value as
+	// non-zero.
+	unspecifiedSlotIndex = ^uint64(0)
 )
 
 var (
@@ -75,6 +80,9 @@ type postForkCommonComponents struct {
 	vm       *VM
 	innerBlk snowman.Block
 	status   choices.Status
+	// slot is used to store the selected slot for this block. It's being used during Accept, and populated
+	// during verifyPostDurangoBlockDelay.
+	slot uint64
 }
 
 // Return the inner block's height
@@ -269,6 +277,7 @@ func (p *postForkCommonComponents) buildChild(
 			vm:       p.vm,
 			innerBlk: innerBlock,
 			status:   choices.Processing,
+			slot:     unspecifiedSlotIndex,
 		},
 	}
 
@@ -366,15 +375,17 @@ func (p *postForkCommonComponents) verifyPostDurangoBlockDelay(
 	var (
 		blkTimestamp = blk.Timestamp()
 		blkHeight    = blk.Height()
-		currentSlot  = proposer.TimeToSlot(parentTimestamp, blkTimestamp)
 		proposerID   = blk.Proposer()
 	)
+	// populate the slot for the block.
+	blk.slot = proposer.TimeToSlot(parentTimestamp, blkTimestamp)
 
+	// find the expected proposer
 	expectedProposerID, err := p.vm.Windower.ExpectedProposer(
 		ctx,
 		blkHeight,
 		parentPChainHeight,
-		currentSlot,
+		blk.slot,
 	)
 	switch {
 	case errors.Is(err, proposer.ErrAnyoneCanPropose):
@@ -389,7 +400,7 @@ func (p *postForkCommonComponents) verifyPostDurangoBlockDelay(
 	case expectedProposerID == proposerID:
 		return true, nil // block should be signed
 	default:
-		return false, fmt.Errorf("%w: slot %d expects %s", errUnexpectedProposer, currentSlot, expectedProposerID)
+		return false, fmt.Errorf("%w: slot %d expects %s", errUnexpectedProposer, blk.slot, expectedProposerID)
 	}
 }
 
@@ -504,3 +515,11 @@ func (p *postForkCommonComponents) shouldBuildSignedBlockPreDurango(
 	p.vm.notifyInnerBlockReady()
 	return false, fmt.Errorf("%w: delay %s < minDelay %s", errProposerWindowNotStarted, delay, minDelay)
 }
+
+// writeAcceptedSlotMetrics use the previously stored slot index and add that to the
+// metrics managed by the vm.
+func (p *postForkCommonComponents) writeAcceptedSlotMetrics() {
+	if p.slot != unspecifiedSlotIndex {
+		p.vm.acceptedBlocksSlotHistogram.Observe(float64(p.slot))
+	}
+}

vms/proposervm/post_fork_block.go

@@ -27,7 +27,11 @@ func (b *postForkBlock) Accept(ctx context.Context) error {
 	if err := b.acceptOuterBlk(); err != nil {
 		return err
 	}
-	return b.acceptInnerBlk(ctx)
+	if err := b.acceptInnerBlk(ctx); err != nil {
+		return err
+	}
+	b.writeAcceptedSlotMetrics()
+	return nil
 }
 
 func (b *postForkBlock) acceptOuterBlk() error {
@@ -106,6 +110,7 @@ func (b *postForkBlock) Options(ctx context.Context) ([2]snowman.Block, error) {
 				vm:       b.vm,
 				innerBlk: innerOption,
 				status:   innerOption.Status(),
+				slot:     unspecifiedSlotIndex,
 			},
 		}
 	}

vms/proposervm/post_fork_option.go

@@ -35,7 +35,11 @@ func (b *postForkOption) Accept(ctx context.Context) error {
 	if err := b.acceptOuterBlk(); err != nil {
 		return err
 	}
-	return b.acceptInnerBlk(ctx)
+	if err := b.acceptInnerBlk(ctx); err != nil {
+		return err
+	}
+	b.writeAcceptedSlotMetrics()
+	return nil
 }
 
 func (b *postForkOption) acceptOuterBlk() error {

vms/proposervm/pre_fork_block.go

@@ -247,6 +247,7 @@ func (b *preForkBlock) buildChild(ctx context.Context) (Block, error) {
 			vm:       b.vm,
 			innerBlk: innerBlock,
 			status:   choices.Processing,
+			slot:     unspecifiedSlotIndex,
 		},
 	}
 

vms/proposervm/vm.go

@@ -99,6 +99,13 @@ type VM struct {
 
 	// lastAcceptedHeight is set to the last accepted PostForkBlock's height.
 	lastAcceptedHeight uint64
+
+	// proposerBuildSlotGauge is the metric gauge used when reporting the current slot block build built.
+	proposerBuildSlotGauge prometheus.Gauge
+
+	// acceptedBlocksSlotHistogram is the metric histogram that is being updated once a block gets accepted with it's corresponding slot.
+	// note that this histogram is being updated by postForkCommonComponents.writeAcceptedSlotMetrics.
+	acceptedBlocksSlotHistogram prometheus.Histogram
 }
 
 // New performs best when [minBlkDelay] is whole seconds. This is because block
@@ -133,6 +140,7 @@ func (vm *VM) Initialize(
 	// TODO: Add a helper for this metrics override, it is performed in multiple
 	//       places.
 	registerer := prometheus.NewRegistry()
+
 	if err := chainCtx.Metrics.Register("proposervm", registerer); err != nil {
 		return err
 	}
@@ -220,6 +228,34 @@ func (vm *VM) Initialize(
 	default:
 		return err
 	}
+
+	vm.proposerBuildSlotGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "block_building_slot",
+			Help: "the post-durango slot in which the block was built",
+		})
+
+	if err = registerer.Register(vm.proposerBuildSlotGauge); err != nil {
+		return err
+	}
+
+	vm.acceptedBlocksSlotHistogram = prometheus.NewHistogram(
+		prometheus.HistogramOpts{
+			Name: "accepted_blocks_slot_histogram",
+			Help: "the post-durango slot in which the block was accepted at",
+			// define the following ranges:
+			// (-inf, 0]
+			// (0, 1]
+			// (1, 2]
+			// (2, inf)
+			// the usage of ".5" before was to ensure we work around the limitation
+			// of comparing floating point of the same numerical value.
+			Buckets: []float64{0.5, 1.5, 2.5},
+		},
+	)
+	if err = registerer.Register(vm.acceptedBlocksSlotHistogram); err != nil {
+		return err
+	}
 	return nil
 }
 
@@ -305,14 +341,16 @@ func (vm *VM) SetPreference(ctx context.Context, preferred ids.ID) error {
 		childBlockHeight = blk.Height() + 1
 		parentTimestamp  = blk.Timestamp()
 		nextStartTime    time.Time
+		proposalSlot     = unspecifiedSlotIndex
 	)
 	if vm.IsDurangoActivated(parentTimestamp) {
 		currentTime := vm.Clock.Time().Truncate(time.Second)
+		proposalSlot = proposer.TimeToSlot(parentTimestamp, currentTime)
 		nextStartTime, err = vm.getPostDurangoSlotTime(
 			ctx,
 			childBlockHeight,
 			pChainHeight,
-			proposer.TimeToSlot(parentTimestamp, currentTime),
+			proposalSlot,
 			parentTimestamp,
 		)
 	} else {
@@ -334,6 +372,13 @@ func (vm *VM) SetPreference(ctx context.Context, preferred ids.ID) error {
 		// until the P-chain's height has advanced.
 		return nil
 	}
+
+	// if we're done bootstrapping, and we have a proposal window slot, update
+	// the metrics accordingly.
+	if (proposalSlot != unspecifiedSlotIndex) && (vm.consensusState == snow.NormalOp) {
+		vm.proposerBuildSlotGauge.Set(float64(proposalSlot))
+	}
+
 	vm.Scheduler.SetBuildBlockTime(nextStartTime)
 
 	vm.ctx.Log.Debug("set preference",
@@ -536,6 +581,7 @@ func (vm *VM) parsePostForkBlock(ctx context.Context, b []byte) (PostForkBlock,
 				vm:       vm,
 				innerBlk: innerBlk,
 				status:   choices.Processing,
+				slot:     unspecifiedSlotIndex,
 			},
 		}
 	} else {
@@ -545,6 +591,7 @@ func (vm *VM) parsePostForkBlock(ctx context.Context, b []byte) (PostForkBlock,
 				vm:       vm,
 				innerBlk: innerBlk,
 				status:   choices.Processing,
+				slot:     unspecifiedSlotIndex,
 			},
 		}
 	}
@@ -590,6 +637,7 @@ func (vm *VM) getPostForkBlock(ctx context.Context, blkID ids.ID) (PostForkBlock
 				vm:       vm,
 				innerBlk: innerBlk,
 				status:   status,
+				slot:     unspecifiedSlotIndex,
 			},
 		}, nil
 	}
@@ -599,6 +647,7 @@ func (vm *VM) getPostForkBlock(ctx context.Context, blkID ids.ID) (PostForkBlock
 			vm:       vm,
 			innerBlk: innerBlk,
 			status:   status,
+			slot:     unspecifiedSlotIndex,
 		},
 	}, nil
 }