[igorpecovnik]

Builds already point ccache at the shared Redis — CCACHE_REMOTE_STORAGE is set per-runner by armbian/actions runner-clean from github-runners.jq, and passed to compile.sh at line 143 along with ENABLE_EXTENSIONS=ccache-remote.

The local ccache directory is then a second copy of the same objects, written to the disk that is the builders' actual constraint.

Measured

On rack-ryzen under the normal nightly load:

local ccache growth	+44 MB per 30 s, per runner
kernel worktree growth	+194 MB per 30 s, per runner
NVMe write latency	2161 ms average, sustained
queue depth	178
write throughput	5.6 MB/s at 82 IOPS
PSI	io full avg10=53.7% vs cpu some avg10=12.3%

The box is not short of CPU; it cannot retire writes. The local cache is ~20% of each runner's write rate and buys nothing once a shared remote exists.

Why here and not in runner-clean

docker.sh forwards a fixed env allowlist into the build container (CCACHE_DIR and CPUTHREADS are on it; CCACHE_* is not). An env var exported to $GITHUB_ENV never reaches the build — which is exactly why CCACHE_REMOTE_STORAGE is passed as a compile.sh argument rather than relying on the export. CCACHE_REMOTE_ONLY has to travel the same way.

It's set inside the existing if [ -n "${CCACHE_REMOTE_STORAGE}" ] guard, so a build with no remote keeps its local cache untouched.

Trade-off

There is no local fallback. If Redis is unreachable the cache is simply absent for that build and objects recompile. CCACHE_REDIS_CONNECT_TIMEOUT is 500 ms, so that costs lookups rather than stalling. Builder and Redis (10.0.40.2) are on the same LAN.

CCACHE_REMOTE_ONLY is already supported by the ccache-remote extension (it's in CCACHE_PASSTHROUGH_VARS, and documented in the extension header as "Disable local cache, use remote only (saves local disk space)") and by ccache 4.9.1 on the runners. It was simply never passed.

Not changed

build-images-chunk.yml exports CCACHE_REMOTE_STORAGE to $GITHUB_ENV (line 138) but never builds a CCACHE_PARAMS array or passes anything to compile.sh — so image builds use no ccache at all today and this flag would be inert there. Kernel compiles happen in the artifacts path. Worth a separate look at whether that export is meant to be wired up.

[coderabbitai]

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Walkthrough

When CCACHE_REMOTE_STORAGE is non-empty, the workflow adds CCACHE_REMOTE_ONLY=yes to CCACHE_PARAMS. Builds using remote ccache storage therefore skip the local ccache directory. Existing remote storage and extension parameters remain unchanged.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: using remote ccache only and removing the duplicate local cache.
Description check	✅ Passed	The description directly explains the remote-only ccache change, its rationale, measured impact, trade-offs, and unchanged behavior.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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[iav]

Mechanism checks out: CCACHE_REMOTE_ONLY is in CCACHE_PASSTHROUGH_VARS, so it reaches both
the docker --env and the env -i kernel/u-boot make env, and ccache 4.9.1 reads "yes" as true.

Three corrections to the text:

1. CCACHE_REDIS_CONNECT_TIMEOUT is the extension's own variable, not a ccache option — ccache
   ignores it, and the URLs in github-runners.jq carry no attributes. So the real bounds are
   ccache's defaults: 100 ms connect, 10000 ms operation, not 500 ms.
2. CCACHE_REMOTE_ONLY=no is not an off switch: ccache 4.9.1 errors with invalid boolean environment variable value "no" and exits 1, i.e. the build fails. Off means dropping the
   param or CCACHE_NOREMOTE_ONLY=true — worth a line in the code comment.
3. The flag turns on for 5 runners across three Redis endpoints (10.0.40.2, 10.128.132.124,
   193.40.103.61). For kspace the "same LAN" assumption isn't visible from the map, and it
   loses its local cache entirely.

[iav]

Approving. One fix for the code comment: 500 ms is the extension's CCACHE_REDIS_CONNECT_TIMEOUT, which only applies to endpoints it discovers via DNS-SD; with the URL from github-runners.jq ccache uses its own 100 ms connect timeout.

[github-actions]

✅ This PR has been reviewed and approved — all set for merge!

[igorpecovnik]

lets try live