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[Engine] strata-sycl.sh drops every STRATA_* variable whose value is 0, so the documented STRATA_PREFILL_MMQ=0 (FP16 prompt path) never reaches the engine; "off" works by accident

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
74/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
bash, cpp, docker
Domain
backend, cli

Research direction

Start with the environment forwarding loop in sycl/serve/strata-sycl.sh and trace how its setting array is built from the config environment. Reproduce with STRATA_PREFILL_MMQ=0 bash -x sycl/serve/strata-sycl.sh --version and inspect the docker run arguments; compare with =off. Done when the documented value 0 reaches the engine as STRATA_PREFILL_MMQ=0 and the launcher’s other switch behavior remains understood.

Written by the indexing model from the issue text.

Description

Area

[Engine] (the SYCL serve path: sycl/serve/strata-sycl.sh, the config's exe on Intel)

Desktop app, Terminal or source?

Source

What happened

The launcher forwards STRATA_* (and ONEAPI_/UR_/IGC_/SYCL_/ZES_) variables into the container, but skips every one whose value is 0 or empty:

for k in "${!setting[@]}"; do
    # the engine tests the switches by presence: a value of 0 (or empty) means "not set", so it is not passed on
    case "${setting[$k]}" in 0|"") ;; *) envs+=(-e "$k=${setting[$k]}") ;; esac
done

That is right for a switch whose unset default is off, and wrong for a three-state switch where unset means "auto". STRATA_PREFILL_MMQ is one: unset = auto on Battlemage, 0 = the FP16 path. 0 is the documented value (docs/INTEL_INT8_EXPERTS.md: "STRATA_PREFILL_MMQ=0: the FP16 path everywhere"; the 0.2.0 release notes), and it is what the engine itself prints at start: int8 prompt experts are on (Battlemage default, auto); STRATA_PREFILL_MMQ=0 turns them off. A config with "env": {"STRATA_PREFILL_MMQ": "0"} (the documented way to give the engine a setting: the server puts the env block into the launcher's environment) starts the auto path anyway, and the log advises the value that was just dropped.

Trace, bash -x sycl/serve/strata-sycl.sh --version:

  • with STRATA_PREFILL_MMQ=0 the exec docker run line carries only the launcher's three defaults: -e STRATA_VERIFY_NO_HOST=1 -e STRATA_VERIFY_DEVICE_PLAN=1 -e STRATA_STAGER_THREADS=12;
  • with STRATA_PREFILL_MMQ=off it also carries -e STRATA_PREFILL_MMQ=off. "off" works only because choose_mode() in sycl/include/strata/prefill/esimd_moe.hpp parses a non-digit string as 0, which no document says.

Seen with the real engine (2026-10-26, v0.2.6 build): an A/B arm whose config env had STRATA_PREFILL_MMQ=0 logged int8 prompt experts are on (Battlemage default, auto) and ran at the auto path's speed (1115 tok/s on a 6,345-token prompt, against 1316 with "off"; the numbers are in the int8 issue I am filing next).

The launcher's own header example, "env": {"STRATA_VERIFY_NO_HOST": "0"}, works by accident: the 0 replaces the launcher's default 1 in the setting array and is then dropped, and the engine's unset default happens to be the same as 0. Other =0 forms the Intel docs give and the launcher cannot deliver: STRATA_I8_FORCE=0, STRATA_I8_WG=0, STRATA_MMVQ_A2=0, STRATA_MMVQ_WIDE_32=0, STRATA_LEND_MIRROR=0, STRATA_ARENA_ALIAS_CHECK=0, STRATA_SPLIT_HEADROOM=0, STRATA_MIRROR_MIB=0 (docs/INTEL.md, INTEL_ARC.md, INTEL_INT8_EXPERTS.md). I did not check which of those have an unset default equal to 0 and which do not.

Expected: a value the config's env block names reaches the engine as written. If some engine switches really are presence-tested (so that K=0 would turn them on), a short list of those names to keep dropping, or a list of the three-state names to pass through, would avoid this; dropping every 0 silently is what bites.

Smallest steps or command that reproduce it
  1. Intel install per docs/INTEL_ARC.md.
  2. In the run config: "env": {"STRATA_PREFILL_MMQ": "0"}; start the server; the engine log says int8 prompt experts are on (Battlemage default, auto).
  3. Change the value to "off": no int8 lines, FP16 timings.
  4. Without a GPU: STRATA_PREFILL_MMQ=0 bash -x sycl/serve/strata-sycl.sh --version 2>&1 | grep 'exec docker run' has no -e STRATA_PREFILL_MMQ; with =off it has.
Reproduction status

Reproduced locally

Strata version

Source v0.2.7.1 (46c152a1), engine 0.1.53 built from it; strata-sycl.sh is identical on main today and was the same on v0.2.6.

Graphics card, memory and system

Intel Arc Pro B70 32 GB · 62 GB RAM · Debian 13 (kernel 7.2.6, xe driver); engine in the strata-sycl-dev container

Model, size and settings

Qwen3.8-Flash-Next IQ3_S (native pack, --stream-experts, --prefill 4096), 256K context, pictures off

Logs

The trace lines above, and the engine's int8 prompt experts are on (Battlemage default, auto); STRATA_PREFILL_MMQ=0 turns them off under a config env of 0.

Dominant language
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