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spec: add backend sampling support for eagle3 #24655

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Merged
ggerganov merged 1 commit into from
Jun 16, 2026
Merged

spec: add backend sampling support for eagle3 #24655

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33 changes: 32 additions & 1 deletion common/speculative.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,9 @@ struct common_speculative_impl_draft_eagle3 : public common_speculative_impl {

std::vector<common_sampler_ptr> smpls;

// backend sampler chain per seq, attached to ctx_dft
std::vector<llama_sampler *> backend_chains;

int32_t n_embd_dec = 0; // draft hidden size
int32_t n_embd_enc = 0; // target_layer_ids_n * target_hidden_size
int32_t n_embd_tgt = 0; // target model hidden size
Expand All @@ -441,7 +444,7 @@ struct common_speculative_impl_draft_eagle3 : public common_speculative_impl {
, params(params.draft)
{
LOG_INF("%s: adding speculative implementation 'draft-eagle3'\n", __func__);
LOG_INF("%s: - n_max=%d, n_min=%d, p_min=%f\n", __func__, params.draft.n_max, params.draft.n_min, params.draft.p_min);
LOG_INF("%s: - n_max=%d, n_min=%d, p_min=%f, backend_sampling=%d\n", __func__, params.draft.n_max, params.draft.n_min, params.draft.p_min, (int) params.draft.backend_sampling);

auto * ctx_tgt = this->params.ctx_tgt;
auto * ctx_dft = this->params.ctx_dft;
Expand Down Expand Up @@ -476,6 +479,22 @@ struct common_speculative_impl_draft_eagle3 : public common_speculative_impl {
s.reset(common_sampler_init(llama_get_model(ctx_dft), sparams));
}

// offload draft sampling to the backend
backend_chains.assign(n_seq, nullptr);
if (this->params.backend_sampling) {
for (llama_seq_id seq_id = 0; seq_id < (llama_seq_id) n_seq; ++seq_id) {
llama_sampler * chain = llama_sampler_chain_init(llama_sampler_chain_default_params());
llama_sampler_chain_add(chain, llama_sampler_init_top_k(10));

if (!llama_set_sampler(ctx_dft, seq_id, chain)) {
LOG_WRN("%s: backend offload failed for seq_id=%d; using CPU sampler\n", __func__, (int) seq_id);
llama_sampler_free(chain);
chain = nullptr;
}
backend_chains[seq_id] = chain;
}
}

// turn on extraction of the target layers' input embeddings
for (uint32_t k = 0; k < target_layer_ids_n; ++k) {
llama_set_embeddings_layer_inp(ctx_tgt, (uint32_t) target_layer_ids[k], true);
Expand All @@ -494,6 +513,18 @@ struct common_speculative_impl_draft_eagle3 : public common_speculative_impl {
}

~common_speculative_impl_draft_eagle3() override {
auto * ctx_dft = this->params.ctx_dft;
for (llama_seq_id seq_id = 0; seq_id < (llama_seq_id) backend_chains.size(); ++seq_id) {
if (backend_chains[seq_id] == nullptr) {
continue;
}
if (ctx_dft) {
llama_set_sampler(ctx_dft, seq_id, nullptr);
}
llama_sampler_free(backend_chains[seq_id]);
}
backend_chains.clear();

if (batch.token != nullptr) {
free(batch.token);
batch.token = nullptr;
Expand Down