linux-arm64: official builds run 2.7–4× slower than pointer-compression builds on Qualcomm Oryon (Snapdragon X2) #67150

Version

v26.12.1 (also seen on v27.0.0-v8-canary202610235563f8f7df)

Platform

Linux abc-a16-win 6.18.54.1-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Tue Oct  6 18:43:37 UTC 2026 aarch64 GNU/Linux
CPU: Qualcomm Snapdragon X2 Elite Extreme X2E94100 (18 Oryon cores), Windows 11 + WSL2

Native Windows arm64 Node on the same machine shows the same slowdown.

Subsystem

build, v8

What steps will reproduce the bug?

On a Snapdragon X2 (Oryon) machine, run the V8 team's Web Tooling Benchmark with the official linux-arm64 build. Then run it with the same release built locally with only pointer compression enabled:

curl -fsSLO https://v8.github.io/web-tooling-benchmark/cli.js
node cli.js                                    # official v26.12.1 linux-arm64

# same release, only pointer compression changed
curl -fsSLO https://nodejs.org/dist/v26.12.1/node-v26.12.1.tar.xz
tar xf node-v26.12.1.tar.xz && cd node-v26.12.1
./configure --experimental-enable-pointer-compression && make -j"$(nproc)"
out/Release/node ../cli.js

How often does it reproduce? Is there a required condition?

Always, on this machine. Required condition: an arm64 build without pointer compression, which is the official default. I don't have other arm64 cores (Apple M-series, Graviton, Ampere) to check whether it is Oryon-specific. On x64 the effect is small (see below).

What is the expected behavior? Why is that the expected behavior?

Official arm64 builds should perform roughly in line with other V8 builds on the same hardware, as they do on x64. There, official Node is within about 2–8% of pointer-compression Node and of Chromium.

What do you see instead?

The official build is 2.7× slower overall and 4× slower on the babel test than the same release with pointer compression. Hardware IPC drops from 3.31 to 1.29.

Web Tooling Benchmark v0.5.3 (same cli.js bundle everywhere; same A16 machine):

x64 reference (i7-13700K, bare-metal Linux): official Node v26.10.0 32.50; unofficial linux-x64-pointer-compression v26.10.0 33.21; Chromium 155 40.89. Node IPC 2.65 vs Chromium 2.89.

Real-world workload: building @mui/material (Babel 8, single-threaded), same machine:

The build output is byte-identical between the two.

Additional information

What was ruled out:

• WSL/virtualisation: native Windows arm64 Node is equally slow, and Chrome in the same WSL instance is fast.
• V8 version: the V8 15.8 canary without pointer compression is still slow.
• JIT tiers and threading: --no-maglev, --no-turbofan, --no-sparkplug, --single-threaded and --no-concurrent-recompilation give unchanged results.
• TLB pressure: transparent_hugepage=always (about 200 MB of the heap in huge pages) gives unchanged results.
• A single hot path: perf shows the same profile shape as x64 (megamorphic LoadIC builtins about 17%, scavenger about 10%). Everything in the process runs at about 40% of the IPC; frontend stalls are 42% vs 28% and backend stalls 30% vs 10%.

I haven't identified why uncompressed tagged values are so much more expensive on Oryon than on x64. Input from V8/arm64 folks would be welcome.

Related: #55735 (Pointer Compression and Isolate Groups). If the 4 GB cage limit still blocks a default switch, possible interim options:

• publish official linux-arm64-pointer-compression (and win-arm64) flavours, like the unofficial x64 one;
• revisit the default on arm64 specifically, given the size of the effect.