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perf: avoid false sharing in block-stm #25766

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optim: avoid false sharing in block-stm
yihuang Jan 12, 2026
e95911e
Merge branch 'main' into false-sharing
Eric-Warehime Jan 12, 2026
b34527e
Merge branch 'main' into false-sharing
aljo242 Jan 13, 2026
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7 changes: 7 additions & 0 deletions blockstm/scheduler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@ import (
"runtime"
"sync"
"sync/atomic"

"golang.org/x/sys/cpu"
)

type TaskKind int
Expand Down Expand Up @@ -32,10 +34,15 @@ func (t *TxDependency) Swap(new []TxnIndex) []TxnIndex {
type Scheduler struct {
blockSize int

_ cpu.CacheLinePad

// An index that tracks the next transaction to try and execute.
executionIdx atomic.Uint64
// A similar index for tracking validation.
validationIdx atomic.Uint64

_ cpu.CacheLinePad
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@yihuang yihuang Jan 12, 2026

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we keep executionIdx and validationIdx in the same cache line, because each executor thread will read both anyway.

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@swift1337 swift1337 Jan 13, 2026

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How did you determine that this yields any perf improvements? Can you attach your local benchmarks here?

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@songgaoye songgaoye Jan 21, 2026 •
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we keep executionIdx and validationIdx in the same cache line, because each executor thread will read both anyway.

I don't think so. Executors read both executionIdx and validationIdx both indices, but they read and write different ones most of the time (executution workers increment executionIdx, validators bump validationIdx).
Keeping them in the same cache line means those writes will constantly invalidate each other’s cache line even though the fields track unrelated counters.
That false sharing is exactly what the padding was supposed to prevent.

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@yihuang yihuang Jan 22, 2026

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we keep executionIdx and validationIdx in the same cache line, because each executor thread will read both anyway.

I don't think so. Executors read both executionIdx and validationIdx both indices, but they read and write different ones most of the time (executution workers increment executionIdx, validators bump validationIdx). Keeping them in the same cache line means those writes will constantly invalidate each other’s cache line even though the fields track unrelated counters. That false sharing is exactly what the padding was supposed to prevent.

I mean at the beginning of the loop, each executor will read both executionIdx and validationIdx to compare them for priority.


// Number of times validationIdx or executionIdx was decreased
decreaseCnt atomic.Uint64
// Number of ongoing validation and execution tasks
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1 change: 1 addition & 0 deletions go.mod
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Expand Up @@ -71,6 +71,7 @@ require (
go.yaml.in/yaml/v3 v3.0.4
golang.org/x/crypto v0.47.0
golang.org/x/sync v0.19.0
golang.org/x/sys v0.39.0
google.golang.org/genproto/googleapis/api v0.0.0-20251202230838-ff82c1b0f217
google.golang.org/grpc v1.78.0
google.golang.org/protobuf v1.36.11
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