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feat(paged): wire ssm_bf16_tau model option for hybrid SSM-state fast mode

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Patch 0026 added the hybrid per-head bf16 SSM-state opt-in as the
ssm_hybrid_tau_thresh cparam + the --ssm-bf16-tau CLI flag (default 0 =
bit-exact f32). Expose it per-model via the LocalAI gallery/model YAML
`options:` list, mirroring the paged_kv / max_batch_tokens setenv hooks.

- grpc-server.cpp: new `ssm_bf16_tau` (alias `ssm_hybrid_tau`) option ->
  setenv(LLAMA_SSM_BF16_TAU) when the value parses to a positive float. It
  does NOT reference the paged-only common_params field, so the turboquant
  fork (which lacks patch 0026) stays byte-clean.
- patch 0026 (common.cpp common_context_params_to_llama): getenv fallback
  feeds cparams.ssm_hybrid_tau_thresh from LLAMA_SSM_BF16_TAU only when the
  --ssm-bf16-tau CLI flag is unset (0). Absent/non-positive env => untouched,
  so stock stays bit-exact; the CLI flag takes precedence when set.
- docs: backend/index.yaml note, docs backends.md, gallery header NOTE
  (referencing A_HYBRID_SSM_RESULTS.md; the 2 NVFP4 entries stay bit-exact).

Byte-safe when unset: with no ssm_bf16_tau option the env is never touched
and the default f32 bit-exact recurrence is preserved. Verified the parse +
consume code paths with a standalone compile-and-run (option string ->
LLAMA_SSM_BF16_TAU -> tau, plus 0 / garbage / CLI-precedence / unset cases).

Assisted-by: Claude:opus-4.8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
This commit is contained in:
Ettore Di Giacinto
2026-06-26 19:51:00 +00:00
parent 9c1c2a6a16
commit b3d3323105
5 changed files with 46 additions and 3 deletions
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21
backend/cpp/llama-cpp/grpc-server.cpp
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@@ -840,6 +840,27 @@ static void params_parse(server_context& /*ctx_server*/, const backend::ModelOpt
// If conversion fails, leave the per-slot cap unset (engine default)
}
}
// --- hybrid per-head bf16 SSM-state precision (patch 0026, qwen3.5 gated-DeltaNet decode) ---
// Opt-in reduced-precision fast mode for the recurrent SSM state: a gated-DeltaNet head whose
// memory length tau_h = 1/(|ssm_a|*softplus(ssm_dt)) tokens exceeds this threshold stays f32;
// faster-decaying heads persist their state as bf16, halving that head's dominant recurrence
// byte stream on decode. The value is the tau threshold in tokens (e.g. 32 / 64); 0 keeps every
// head f32 (the bit-exact default). Set BEFORE context init via LLAMA_SSM_BF16_TAU, consumed in
// common_context_params_to_llama (patch 0026) only when the --ssm-bf16-tau CLI flag is unset.
// Unset / non-positive => env untouched, so stock stays byte-identical and bit-exact (an
// externally exported LLAMA_SSM_BF16_TAU still works as an escape hatch). NOTE: this mode is
// NOT bit-exact (~91% same-top-p ceiling); see patches/paged/A_HYBRID_SSM_RESULTS.md.
} else if (!strcmp(optname, "ssm_bf16_tau") || !strcmp(optname, "ssm_hybrid_tau")) {
if (optval != NULL) {
try {
float tau = std::stof(optval_str);
if (tau > 0.0f) {
setenv("LLAMA_SSM_BF16_TAU", std::to_string(tau).c_str(), 1);
}
} catch (const std::exception& e) {
// If conversion fails, leave the threshold unset (bit-exact f32 default)
}
}
} else if (!strcmp(optname, "n_ctx_checkpoints") || !strcmp(optname, "ctx_checkpoints")) {
if (optval != NULL) {
try {