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perf(build): enable ARMv8 hardware AES-GCM — every aarch64 client ran software crypto

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RustCrypto aes 0.8.x and polyval 0.6.x gate their ARMv8 AES / PMULL
paths behind --cfg aes_armv8 / --cfg polyval_armv8 on aarch64 (x86_64
runtime-detects AES-NI with no flag, which is why hosts never showed
it). Without the cfgs every Apple and Android client decrypted the
media plane in SOFTWARE: 240 MiB/s/core measured on an M3 Ultra —
7 µs per 1.4 KB datagram, single-handedly capping receive throughput
at ~1.57 Gbps wire on both host pairs.

Workspace .cargo/config.toml sets both cfgs for
cfg(target_arch = "aarch64"); detection stays runtime (cpufeatures)
with a safe soft fallback. open_in_place: 240 MiB/s -> 2.42 GiB/s
(10.3x). Live sweep .173 -> M3 Ultra over 10GbE: ceiling 1572 ->
4830 Mbps wire, zero loss through a 3.5 Gbps target; the .21 pair now
saturates its physical 2.4 Gbps fabric exactly.

No in-tree build path sets RUSTFLAGS (xcframework + gradle checked),
so the config reaches all client builds; a lane that sets RUSTFLAGS
overrides config rustflags entirely and must carry the cfgs itself
(noted in the file). Shipping Apple/Android binaries stay on software
crypto until rebuilt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Enrico Bühler
2026-07-14 19:08:35 +02:00
parent ed0ce5dc6d
commit 160914c48b
1 changed files with 18 additions and 0 deletions
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.cargo/config.toml
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# Workspace-wide build flags.
#
# aes_armv8: RustCrypto's `aes` 0.8.x enables ARMv8-Crypto hardware AES on aarch64 only behind
# this cfg (x86_64 AES-NI is runtime-detected with no flag; the 0.9 line will make aarch64
# automatic too). Without it every aarch64 client (all Apple + virtually all Android) ran
# SOFTWARE AES on the per-packet decrypt path — measured 2026-07-14 on an M3 Ultra at
# ~240 MiB/s/core (~7 µs per 1.4 KB datagram), which single-handedly capped receive throughput
# at ~1.57 Gbps wire. The cfg still runtime-detects via `cpufeatures`, so a chip without the
# extensions falls back safely.
#
# NOTE: a RUSTFLAGS environment variable OVERRIDES config rustflags entirely — build scripts /
# CI lanes that set RUSTFLAGS for aarch64 targets (cargo-ndk, xcframework) must carry
# `--cfg aes_armv8` themselves.
# polyval_armv8: same story for GCM's other half — `polyval` 0.6.x gates its PMULL (carry-less
# multiply) GHASH path behind this cfg on aarch64. AES alone took open_in_place from 240 to
# ~790 MiB/s on the M3 Ultra; software GHASH still dominated until this flag joined it.
[target.'cfg(target_arch = "aarch64")']
rustflags = ["--cfg", "aes_armv8", "--cfg", "polyval_armv8"]