From d3986b53b908d784842c750c674d695442560e80 Mon Sep 17 00:00:00 2001
From: Kyle Carberry <kyle@coder.com>
Date: Tue, 10 Mar 2026 08:54:32 -0700
Subject: [PATCH] perf(ci): use fast zstd compression for non-release CI builds
 (#22907)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

## Problem

The `build` job on `main` takes ~7m28s for the Build step alone (~13m
total). Analysis of 10 recent CI runs on `main` shows the zstd
compression of the slim binary archive is the second largest bottleneck:

| Phase | Avg Duration | % of Build Step |
|-------|-------------|----------------|
| Fat Go builds (7 binaries w/ embed) | ~205s | 45.8% |
| **zstd compression (`-22 --ultra`)** | **~123s** | **27.4%** |
| Parallel block (vite + slim Go builds) | ~65s | 14.5% |
| Packaging + signing | ~55s | 12.3% |

The `zstd -22 --ultra` setting compresses a ~350 MB tar to ~71 MB, but
it is **single-threaded** and takes ~102s on 8-core CI runners. Adding
`-T8` does not help at level 22 — it remains CPU-bound on a single
thread.

## Solution

Use `zstd -6 -T0` (multithreaded, auto-detect cores) for non-release CI
builds. Release builds (`CODER_RELEASE=true`) continue using `-22
--ultra`.

### Benchmarks (349 MB slim binary tar, 8 cores)

| Setting | Wall Time | Output Size | Use Case |
|---------|----------|------------|----------|
| `-22 --ultra` | **102.4s** | 71 MB | Release builds |
| `-6 -T0` | **0.8s** | 94 MB | CI builds (new) |
| `-6` | 2.4s | 94 MB | Local dev (unchanged) |

The 23 MB size increase is negligible for the main branch preview images
(`ghcr.io/coder/coder-preview:main`). The archive is embedded in fat
binaries and extracted once by the agent at startup — decompression time
is identical regardless of compression ratio.

### Expected impact

~120s savings on the Build step, bringing it from ~7m28s to ~5m30s.

## Verification

All three code paths confirmed:
- `CODER_RELEASE=true CI=true` → `-22 --ultra` ✅
- `CI=true` (no `CODER_RELEASE`) → `-6 -T0` ✅
- Local (no `CI`) → `-6` ✅
- `CODER_RELEASE=false CI=true` (dry run) → `-6 -T0` ✅
---
 Makefile | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 2421a6ddf7..f6f9f21a47 100644
--- a/Makefile
+++ b/Makefile
@@ -118,11 +118,14 @@ POSTGRES_IMAGE   ?= us-docker.pkg.dev/coder-v2-images-public/public/postgres:$(P
 # parallelism. Override: make pre-push PARALLEL_JOBS=8
 PARALLEL_JOBS ?= $(shell n=$$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 8); echo $$(( n / 4 > 2 ? n / 4 : 2 )))
 
-# Use the highest ZSTD compression level in CI.
-ifdef CI
+# Use the highest ZSTD compression level in release builds to
+# minimize artifact size. For non-release CI builds (e.g. main
+# branch preview), use multithreaded level 6 which is ~99% faster
+# at the cost of ~30% larger archives.
+ifeq ($(CODER_RELEASE),true)
 ZSTDFLAGS := -22 --ultra
 else
-ZSTDFLAGS := -6
+ZSTDFLAGS := -6 -T0
 endif
 
 # Common paths to exclude from find commands, this rule is written so