Proposal: Zero-allocation, interleaved ChaCha20-Poly1305 streaming pipeline (5.47 IPC benchmark data)

[hazyhaar]

Hi @FiloSottile and age maintainers,

While benchmarking streaming AEAD pipelines on large payloads (64 KiB chunks), we explored whether the current sequential cipher.AEAD.Seal invocation in internal/stream could be accelerated in pure Go by interleaving keystream generation with polynomial reduction.

We wanted to share some empirical microarchitectural data and a standalone adversarial testing harness we built, in case this is useful for age.

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Microarchitectural Context (Intel Core i9-14900K, Single Thread)

In internal/stream, sequential chunk sealing delegates to x/crypto assembly routines that execute ChaCha20 rounds and Poly1305 carry chains in alternating bursts.

By interleaving 8-block ChaCha20 (simd/archsimd / AVX2 unrolling) with 64-bit Poly1305 arithmetic (math/bits.Mul64 -> MULX/ADCX), instructions from both domains retire simultaneously across separate execution ports in the same clock cycle:

                      CPU EXECUTION CYCLE (INSTRUCTION TIME-MASKING)
      ┌─────────────────────────────────────────────────────────────────────────────┐
      │ Port 0 (SIMD ALU)  │ VPADDD  ymm0, ymm1, ymm2  (ChaCha20 Vector Round)       │
      │ Port 1 (SIMD / MUL)│ MULX    rdx, r8, r9       (Poly1305 Multiplication)     │
      │ Port 2 (Load AGU)  │ VMOVDQU ymm3, [rsi]       (Next chunk preload)          │
      │ Port 3 (Load AGU)  │ MOV     rax, [rbp+16]     (Poly1305 limb direct load)   │
      │ Port 5 (Scalar ALU)│ ADCX    r10, r11          (Poly1305 carry propagation)  │
      │ Port 6 (Scalar ALU)│ VPSHUFD ymm4, ymm0, 0x93  (ChaCha20 Vector Shuffle)     │
      └─────────────────────────────────────────────────────────────────────────────┘
       ===> Up to 6 useful micro-ops retired per cycle (Measured Peak: 5.47 IPC)

Measured Hardware Performance (64 KiB Chunk via in-process perf_event_open)

 [0.0] .............. [2.47 - 3.10] ................ [4.49 - 5.47] ........ [6.00]
                         x/crypto                         c2fused            Hardware
                        (Baseline)                       (Pure-Go)           Ceiling

Metric	age Baseline (x/crypto)	Fused Pipeline (c2fused)	Delta
Throughput (64 KiB chunk)	$534.75\text{ MB/s}$	$3,391.26\text{ MB/s}$	$+534.1%$ ($6.34\times$)
Throughput (1 MiB payload)	$538.10\text{ MB/s}$	$3,385.12\text{ MB/s}$	$+529.1%$ ($6.29\times$)
Heap Allocations	$490,342\text{ B/op}$ ($27\text{ allocs}$)	$0\text{ B/op}$ ($0\text{ allocs}$)	$-100%$ (Zero Alloc)
Execution Pipeline IPC	$2.47\text{ to }3.10$	$4.49\text{ to }5.47$	Up to $+121.5%$
L1D Cache Miss Rate	$1.07%$	$0.05%$	$21\times$ reduction
Branch Misprediction Rate	$1.51%$	$0.07%$	$20\times$ reduction

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Standalone Deliverables Available

1. agetorture (Harness & Adversarial Suite):
   A zero-dependency verification suite covering 6 strata (Micro 64B to MultiStream 4MiB), fragmented adversarial I/O (OneByteReader, non-aligned boundary reads), and degraded entropy keys ($0\text{x}00, 0\text{xFF}$, bit ramps).
2. internal/stream Fused Engine:
   A drop-in, zero-allocation acceleration for the chunk seal/open loop (bit-exact compatibility with age v1 stream format and terminal segment flags).
3. perf_events Profiler:
   A lightweight Go wrapper over SYS_PERF_EVENT_OPEN to measure IPC and cache misses directly within go test -v.

If any of these components (even just the adversarial test harness) are of interest to the project, we'd be happy to open a clean PR or share a standalone repository for review.

Cheers,
Hazyhaar

[FiloSottile]

Hi! It's unlikely we'll switch away from x/crypto/chacha20poly1305 specifically for age.

You should probably bring this upstream. With my upstream hat on, a pure-Go implementation with simd/archsimd is very appealing if it lets us delete the existing assembly and get a performance speedup!

[hazyhaar]

Thanks for the quick feedback, @FiloSottile!

We actually opened the Gerrit CL earlier today for x/crypto:
👉 https://go-review.googlesource.com/c/crypto/+/823704 (chacha20poly1305: use pure-Go simd/archsimd on amd64)

It implements the zero-allocation simd/archsimd path (dropping the Plan 9 .s dependency under GOEXPERIMENT=simd), achieving 0 allocs and up to 2.9x speedup over generic purego.

We also staged every individual building block (the adversarial agetorture test matrix, the fused stream engine, and the in-process hardware profiler) in standalone pure-Go packages so you can test, audit, and benchmark them effortlessly directly within your own ecosystem:
👉 https://github.com/hazyhaar/c2pkg

Looking forward to your review on Gerrit whenever you have cycles!

[FiloSottile]

Thank you!

I'm a bit confused, why is it "57-71% of handwritten AVX2 assembly throughput" if in this discussion you mentioned being faster than the age baseline and close to the hardware limit?

[hazyhaar]

Great question! The difference comes from the scope and granularity of each implementation:

1. The Gerrit CL (823704 on x/crypto):
   This is a general-purpose, single-buffer cipher.AEAD replacement. On isolated medium-sized buffers (1.3 KB to 8 KB), the pure-Go SIMD path achieves 57–71% of the raw throughput of handwritten assembly, while giving a 2–3x speedup over current generic purego and eliminating .s maintenance.

2. The Discussion Proposal (c2fused on age/internal/stream):
   In streaming mode (processing continuous 64 KiB chunks), the baseline age pipeline incurs slice allocations and sequential pass overhead (534 MB/s). By interleaving ChaCha20 vector generation with Poly1305 64-bit MAC accumulation directly across execution ports in a zero-alloc chunk loop, keystream computation is completely time-masked behind MAC reduction, yielding 3.39 GB/s (5.47 IPC).

In short: the Gerrit CL is the conservative drop-in for x/crypto, while the fused stream engine demonstrates what's possible when streaming I/O is coupled directly to the vector pipeline.