feat: add linear and attention scale overrides (#1964)

2026-09-21 13:38:01 -05:00 · 2026-09-12 01:41:28 +08:00
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+# Troubleshooting
+
+## Completely black or white images or videos / NaNs
+
+Some ggml backends can encounter numerical overflow during inference, producing
+NaN (not-a-number) values. This can result in completely black or white images or videos.
+Whether it happens can depend on the backend, device, model, and weight format.
+
+Known overflow issues have been addressed as far as possible, but the maintainer
+has limited hardware and cannot test every combination. Some cases may therefore
+still need a manual workaround.
+
+These options are supported by both `sd-cli` and `sd-server`. If you encounter
+this problem, add them to your CLI generation command or server startup command:
+
+```sh
+--linear-scale 0.0078125 --attn-scale 0.0078125
+```
+
+For `sd-server`, restart the server after changing these startup options. Run the
+same prompt and seed again to see whether the output recovers. If the problem
+persists, try smaller positive values, for example:
+
+```sh
+--linear-scale 0.00390625 --attn-scale 0.00390625
+```
+
+These options reduce intermediate values and compensate afterwards to preserve
+the intended output scale:
+
+- `--linear-scale` scales Linear inputs before matrix multiplication and rescales
+  the result.
+- `--attn-scale` scales attention keys and values (K/V). It takes effect only in
+  the Flash Attention path, where `--fa` or `--diffusion-fa` is enabled and the
+  backend supports it.
+
+The two values can be set independently and apply across model components. The
+default `0` preserves each model's built-in settings; `1` explicitly disables the
+corresponding scaling. Overrides must be finite positive values. C API users can
+set `linear_scale` and `attn_scale` in `sd_ctx_params_t`.
+
+If the problem persists after trying the relevant steps above,
+[submit a bug report](https://github.com/leejet/stable-diffusion.cpp/issues/new?template=bug_report.yml).
+Include your full command, backend and hardware, model and weight format, logs,
+and the scale values you tried with their results.