spec : add probabilistic sampling for simple draft and MTP (#27694)

* Make the drafter probabilistic and the target verify by rejection sampling

* Drop stale spec_draft_q before drafting

* Fallback to argmax sampling for grammar-constrained requests and adding flag for enabling probabilistic draft sampling. Default flag value is greedy.

* Support grammar-constrained requests in rejection sampling

* Fix - renormalize distribution after masking

* copy rng on sampler copy and re-accept drafted tokens on replay

* Fix draft sampler sharing the target's rng stream

* Simplify the rejection sampler's inputs and move replay to the server

* Truncate the draft candidates along with the draft

---------

Co-authored-by: praneshgo <227579474+praneshgo@users.noreply.github.com>
Co-authored-by: Pranesh Gonegandla <pgonegandla@nvidia.com>

common/arg.cpp

@@ -4209,6 +4209,21 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
             params.speculative.draft.backend_sampling = value;
         }
     ).set_spec().set_examples({LLAMA_EXAMPLE_SPECULATIVE, LLAMA_EXAMPLE_SERVER, LLAMA_EXAMPLE_CLI}).set_env("LLAMA_ARG_SPEC_DRAFT_BACKEND_SAMPLING"));
+    add_opt(common_arg(
+        {"--spec-draft-sampling"}, "{greedy,probabilistic}",
+        string_format("how the draft is sampled: greedy takes its argmax, probabilistic samples it and has "
+                      "the target verify by rejection sampling (default: %s)",
+                      params.speculative.draft.probabilistic ? "probabilistic" : "greedy"),
+        [](common_params & params, const std::string & value) {
+            if (value == "greedy") {
+                params.speculative.draft.probabilistic = false;
+            } else if (value == "probabilistic") {
+                params.speculative.draft.probabilistic = true;
+            } else {
+                throw std::invalid_argument("invalid value, must be one of: greedy, probabilistic");
+            }
+        }
+    ).set_spec().set_examples({LLAMA_EXAMPLE_SPECULATIVE, LLAMA_EXAMPLE_SERVER, LLAMA_EXAMPLE_CLI}).set_env("LLAMA_ARG_SPEC_DRAFT_SAMPLING"));
     add_opt(common_arg(
         {"--spec-draft-device", "-devd", "--device-draft"}, "<dev1,dev2,..>",
         "comma-separated list of devices to use for offloading the draft model (none = don't offload, default: follows --device)\n"

common/common.h

@@ -333,6 +333,8 @@ struct common_params_speculative_draft {
 
     bool backend_sampling = true; // offload draft sampling to the backend (default: on)
 
+    bool probabilistic = false; // sample the draft and verify by rejection, instead of argmax and match
+
     common_params_model mparams;
 
     llama_context * ctx_tgt = nullptr;

common/sampling.cpp

@@ -12,6 +12,7 @@
 #include <climits>
 #include <cmath>
 #include <cstring>
+#include <random>
 #include <unordered_map>
 #include <vector>
 
@@ -121,6 +122,9 @@ struct common_sampler {
 
     llama_token_data_array cur_p;
 
+    // for rejection sampling; independent of the draft, or the target distribution is not preserved
+    std::mt19937 rng;
+
     void reset() {
         prev.clear();
 
@@ -432,6 +436,8 @@ struct common_sampler * common_sampler_init(
         /* .prev    = */ ring_buffer<llama_token>(std::max(32, params.n_prev)),
         /* .cur     = */ {},
         /* .cur_p   = */ {},
+        // mix it, the chain and the draft are seeded from this one too
+        /* .rng     = */ std::mt19937(llama_sampler_get_seed(chain) ^ 0x9e3779b9u),
     };
 
     return result;
@@ -515,6 +521,7 @@ struct common_sampler * common_sampler_clone(common_sampler * gsmpl) {
         /* .prev    = */ gsmpl->prev,
         /* .cur     = */ gsmpl->cur,
         /* .cur_p   = */ gsmpl->cur_p,
+        /* .rng     = */ gsmpl->rng,
     };
 }
 
@@ -535,6 +542,7 @@ void common_sampler_copy(const common_sampler * src, common_sampler * dst) {
     dst->cur        = src->cur;
     dst->cur_p      = src->cur_p;
     dst->cur_p.data = src->cur_p.data ? dst->cur.data() : nullptr; // re-point to dst's buffer
+    dst->rng        = src->rng;
     dst->t_total_us = src->t_total_us;
 }
 
@@ -709,6 +717,124 @@ std::vector<llama_token> common_sampler_sample_and_accept_n(struct common_sample
     return result;
 }
 
+static float prob_of(const llama_token_data * data, size_t n, llama_token id) {
+    for (size_t k = 0; k < n; ++k) {
+        if (data[k].id == id) {
+            return data[k].p;
+        }
+    }
+    return 0.0f;
+}
+
+// Accept a drafted token with probability min(1, p/q), else draw from norm(max(0, p - q)).
+// Preserves the target distribution exactly, and accepts more often than matching does when the
+// draft samples instead of taking its argmax.
+std::vector<llama_token> common_sampler_sample_and_accept_n_rejection(struct common_sampler * gsmpl, struct llama_context * ctx, const std::vector<int> & idxs, const llama_tokens & draft, const std::vector<std::vector<llama_token_data>> & draft_q, bool grammar_first) {
+    GGML_ASSERT(idxs.size()    == draft.size() + 1 && "idxs.size() must be draft.size() + 1");
+    GGML_ASSERT(draft_q.size() == draft.size() && "draft_q must have one entry per draft token");
+
+    std::vector<llama_token> result;
+    result.reserve(idxs.size());
+
+    // draws come from the sampler's own stream, so they stay independent of what was drafted
+    std::uniform_real_distribution<float> uni(0.0f, 1.0f);
+
+    std::vector<llama_token_data> residual;
+
+    std::vector<llama_token_data> cand; // candidate array masked by the grammar, if there is one
+
+    size_t i = 0;
+    for (; i < draft.size(); i++) {
+        // leaves the target distribution in the candidate array
+        const llama_token id_tgt = common_sampler_sample(gsmpl, ctx, idxs[i], grammar_first);
+
+        const auto * cur_p = common_sampler_get_candidates(gsmpl, true);
+        const auto & q     = draft_q[i];
+
+        const bool masked = !grammar_first && grammar_should_apply(gsmpl);
+        if (masked) {
+            cand.assign(cur_p->data, cur_p->data + cur_p->size);
+            llama_token_data_array arr = { cand.data(), cand.size(), -1, false };
+            llama_sampler_apply(gsmpl->grmr, &arr);
+        }
+
+        // a candidate the grammar rejects carries no probability, whatever the target thinks
+        auto p_raw = [&](size_t k) {
+            return masked && cand[k].logit == -INFINITY ? 0.0f : cur_p->data[k].p;
+        };
+
+        // masking drops probability mass, so rescale what is left or the residual is over-weighted
+        float p_sum = 0.0f;
+        if (masked) {
+            for (size_t k = 0; k < cur_p->size; ++k) {
+                p_sum += p_raw(k);
+            }
+        }
+
+        const float p_norm = masked && p_sum > 0.0f ? 1.0f/p_sum : 1.0f;
+
+        auto p_of = [&](size_t k) {
+            return p_raw(k)*p_norm;
+        };
+
+        // q_x is never 0 for a token the draft produced, but guard the divide
+        const float q_x = prob_of(q.data(), q.size(), draft[i]);
+
+        float p_x = 0.0f;
+        for (size_t k = 0; k < cur_p->size; ++k) {
+            if (cur_p->data[k].id == draft[i]) {
+                p_x = p_of(k);
+                break;
+            }
+        }
+
+        if (q_x > 0.0f && (p_x >= q_x || uni(gsmpl->rng) < p_x / q_x)) {
+            common_sampler_accept(gsmpl, draft[i], true);
+            result.push_back(draft[i]);
+            continue;
+        }
+
+        // rejected: tokens outside q's support keep all of p
+        residual.clear();
+        float sum = 0.0f;
+        for (size_t k = 0; k < cur_p->size; ++k) {
+            const float r = p_of(k) - prob_of(q.data(), q.size(), cur_p->data[k].id);
+            if (r > 0.0f) {
+                residual.push_back({ cur_p->data[k].id, 0.0f, r });
+                sum += r;
+            }
+        }
+
+        llama_token id = id_tgt;
+        if (sum > 0.0f) {
+            float u = uni(gsmpl->rng) * sum;
+            id = residual.back().id;
+            for (const auto & e : residual) {
+                u -= e.p;
+                if (u <= 0.0f) {
+                    id = e.id;
+                    break;
+                }
+            }
+        }
+
+        common_sampler_accept(gsmpl, id, true);
+        result.push_back(id);
+
+        break;
+    }
+
+    if (i == draft.size()) {
+        const llama_token id = common_sampler_sample(gsmpl, ctx, idxs[i], grammar_first);
+
+        common_sampler_accept(gsmpl, id, true);
+
+        result.push_back(id);
+    }
+
+    return result;
+}
+
 std::vector<llama_token> common_sampler_sample_and_accept_n(struct common_sampler * gsmpl, struct llama_context * ctx, const llama_tokens & draft, bool grammar_first) {
     std::vector<int> idxs(draft.size() + 1);
     for (size_t i = 0; i < idxs.size(); ++i) {

common/sampling.h

@@ -85,6 +85,9 @@ llama_token common_sampler_sample(struct common_sampler * gsmpl, struct llama_co
 //
 std::vector<llama_token> common_sampler_sample_and_accept_n(struct common_sampler * gsmpl, struct llama_context * ctx, const std::vector<int> & idxs, const llama_tokens & draft, bool grammar_first = false);
 
+// as above, but verifies by rejection sampling; draft_q holds the draft's candidates per token
+std::vector<llama_token> common_sampler_sample_and_accept_n_rejection(struct common_sampler * gsmpl, struct llama_context * ctx, const std::vector<int> & idxs, const llama_tokens & draft, const std::vector<std::vector<llama_token_data>> & draft_q, bool grammar_first = false);
+
 // assume idxs == [ 0, 1, 2, ..., draft.size() ]
 std::vector<llama_token> common_sampler_sample_and_accept_n(struct common_sampler * gsmpl, struct llama_context * ctx, const llama_tokens & draft, bool grammar_first = false);
 

common/speculative.cpp

@@ -30,6 +30,45 @@
 #define SPEC_VOCAB_MAX_SIZE_DIFFERENCE  128
 #define SPEC_VOCAB_CHECK_START_TOKEN_ID 5
 
+// Rebuild seq_id's draft sampler at the target's temperature: rejection weighs q against p, so
+// both have to sample alike. Only temp and seed carry over; the draft keeps its own top_k.
+static void spec_retune(
+        std::vector<common_sampler_ptr> & smpls,
+        std::vector<common_params_sampling> & cfg,
+        const llama_model * model,
+        llama_seq_id seq_id,
+        float temp,
+        uint32_t seed) {
+    if (cfg.size() != smpls.size()) {
+        const size_t n_old = cfg.size();
+        cfg.resize(smpls.size());
+
+        // the initial sampler has no temperature, so no request may match the cache and skip a rebuild
+        for (size_t i = n_old; i < cfg.size(); ++i) {
+            cfg[i].temp = NAN;
+        }
+    }
+
+    auto & cur = cfg[seq_id];
+
+    if (cur.temp == temp && cur.seed == seed) {
+        return;
+    }
+
+    cur.temp = temp;
+    cur.seed = seed;
+
+    common_params_sampling sparams;
+    sparams.no_perf  = false;
+    sparams.top_k    = 10;
+    sparams.temp     = cur.temp;
+    // must be explicit, the default reseeds at random; mixed so it differs from the target's
+    sparams.seed     = cur.seed == LLAMA_DEFAULT_SEED ? cur.seed : cur.seed ^ 0x85ebca6bu;
+    sparams.samplers = { COMMON_SAMPLER_TYPE_TOP_K, COMMON_SAMPLER_TYPE_TEMPERATURE };
+
+    smpls[seq_id].reset(common_sampler_init(model, sparams));
+}
+
 const std::map<std::string, common_speculative_type> common_speculative_type_from_name_map = {
     {"none",          COMMON_SPECULATIVE_TYPE_NONE},
     {"draft-simple",  COMMON_SPECULATIVE_TYPE_DRAFT_SIMPLE},
@@ -187,6 +226,8 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
 
     std::vector<common_sampler_ptr> smpls;
 
+    std::vector<common_params_sampling> smpls_cfg;
+
     common_speculative_impl_draft_simple(const common_params_speculative & params, uint32_t n_seq)
         : common_speculative_impl(COMMON_SPECULATIVE_TYPE_DRAFT_SIMPLE, n_seq, params.draft.n_max)
         , params(params.draft)
@@ -255,8 +296,9 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
         }
     }
 
-    void begin(llama_seq_id /*seq_id*/, const llama_tokens & /*prompt*/) override {
-        // noop
+    void begin(llama_seq_id seq_id, const llama_tokens & /*prompt*/) override {
+        // reset here rather than per round, or two identical requests differ
+        common_sampler_reset(smpls[seq_id].get());
     }
 
     bool process(const common_batch & batch_in) override {
@@ -323,7 +365,20 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
 
             n_drafting++;
             drafting[seq_id] = true;
-            common_sampler_reset(smpls[seq_id].get());
+            // greedy drafting leaves no candidates behind, so the verifier falls back to sample-and-match
+            if (!params.probabilistic) {
+                dp.result_q = nullptr;
+            }
+
+            // result_q is only set when the caller wants rejection, so it also gates the retune
+            if (dp.result_q) {
+                spec_retune(smpls, smpls_cfg, llama_get_model(ctx_dft), seq_id, dp.temp, dp.seed);
+            }
+
+            // a reset reseeds the chain, which breaks probabilistic drafting
+            if (!dp.result_q) {
+                common_sampler_reset(smpls[seq_id].get());
+            }
 
             batch.add(dp.id_last, dp.pos0, seq_id, true);
         }
@@ -348,7 +403,7 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
 
                 auto * smpl = smpls[seq_id].get();
 
-                common_sampler_sample(smpl, ctx_dft, i_batch, true);
+                const llama_token id_sampled = common_sampler_sample(smpl, ctx_dft, i_batch, true);
                 ++i_batch;
 
                 const auto * cur_p = common_sampler_get_candidates(smpl, true);
@@ -360,7 +415,7 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
                 }
 
                 // add drafted token for each sequence
-                const llama_token id = cur_p->data[0].id;
+                const llama_token id = dparams.at(seq_id).result_q ? id_sampled : cur_p->data[0].id;
 
                 // only collect very high-confidence draft tokens
                 if (cur_p->data[0].p < params.p_min) {
@@ -377,6 +432,10 @@ struct common_speculative_impl_draft_simple : public common_speculative_impl {
 
                 result.push_back(id);
 
+                if (dp.result_q) {
+                    dp.result_q->emplace_back(cur_p->data, cur_p->data + cur_p->size);
+                }
+
                 if ((params.n_max <= (int) result.size()) ||
                     (dp.n_max > 0 && dp.n_max <= (int) result.size())) {
                     drafting[seq_id] = false;
@@ -1335,6 +1394,8 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
 
     std::vector<common_sampler_ptr> smpls;
 
+    std::vector<common_params_sampling> smpls_cfg;
+
     // backend sampler chain per seq, attached to ctx_dft
     std::vector<llama_sampler *> backend_chains;
 
@@ -1455,6 +1516,9 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
     }
 
     void begin(llama_seq_id seq_id, const llama_tokens & prompt) override {
+        // reset here rather than per round, or two identical requests differ
+        common_sampler_reset(smpls[seq_id].get());
+
         const int32_t N = (int32_t) prompt.size();
         if (N <= 0) {
             return;
@@ -1599,7 +1663,20 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
 
             n_drafting++;
             drafting[seq_id] = true;
-            common_sampler_reset(smpls[seq_id].get());
+            // greedy drafting leaves no candidates behind, so the verifier falls back to sample-and-match
+            if (!params.probabilistic) {
+                dp.result_q = nullptr;
+            }
+
+            // result_q is only set when the caller wants rejection, so it also gates the retune
+            if (dp.result_q) {
+                spec_retune(smpls, smpls_cfg, llama_get_model(ctx_dft), seq_id, dp.temp, dp.seed);
+            }
+
+            // a reset reseeds the chain, which breaks probabilistic drafting
+            if (!dp.result_q) {
+                common_sampler_reset(smpls[seq_id].get());
+            }
 
             const int32_t idx = batch.add(dp.id_last, dp.pos0, seq_id, true);
             batch.set_embd(idx, { pending_h[seq_id].data(), 1, (size_t) n_embd });
@@ -1648,7 +1725,7 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
 
                 auto * smpl = smpls[seq_id].get();
 
-                common_sampler_sample(smpl, ctx_dft, i_last[seq_id], true);
+                const llama_token id_sampled = common_sampler_sample(smpl, ctx_dft, i_last[seq_id], true);
                 const float * h_row = llama_get_embeddings_nextn_ith(ctx_dft, i_last[seq_id]);
 
                 const auto * cur_p = common_sampler_get_candidates(smpl, true);
@@ -1660,7 +1737,7 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
                 }
 
                 // add drafted token for each sequence
-                const llama_token id = cur_p->data[0].id;
+                const llama_token id = dparams.at(seq_id).result_q ? id_sampled : cur_p->data[0].id;
 
                 // only collect very high-confidence draft tokens
                 if (cur_p->data[0].p < params.p_min) {
@@ -1677,6 +1754,10 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
 
                 result.push_back(id);
 
+                if (dp.result_q) {
+                    dp.result_q->emplace_back(cur_p->data, cur_p->data + cur_p->size);
+                }
+
                 if (params.n_max <= (int) result.size()) {
                     drafting[seq_id] = false;
                     n_drafting--;
@@ -2833,6 +2914,11 @@ void common_speculative_draft(common_speculative * spec) {
                     if (!result.empty() && (int) result.size() > dp.n_max) {
                         SPC_DBG("truncating draft to %d tokens\n", dp.n_max);
                         result.resize(dp.n_max);
+
+                        // the candidates are one per drafted token and must be cut with them
+                        if (dp.result_q) {
+                            dp.result_q->resize(dp.n_max);
+                        }
                     }
                 }
 

common/speculative.h

@@ -69,6 +69,13 @@ struct common_speculative_draft_params {
 
     // the generated draft from the last _draft() call
     llama_tokens * result;
+
+    // candidate distribution per drafted token; set it to make draft-simple and draft-mtp sample
+    std::vector<std::vector<llama_token_data>> * result_q = nullptr;
+
+    // the target's temp and seed, read only when the drafter samples probabilistically
+    float    temp = 1.0f;
+    uint32_t seed = LLAMA_DEFAULT_SEED;
 };
 
 common_speculative_draft_params & common_speculative_get_draft_params(common_speculative * spec, llama_seq_id seq_id);

tools/server/server-context.cpp

@@ -53,6 +53,31 @@ static common_speculative_output_limits server_output_limits(const common_params
     return result;
 }
 
+// a checkpoint restore dropped tokens the target had accepted - re-accept them rather than verify again
+static std::vector<llama_token> server_accept_replay(
+        common_sampler * smpl,
+        llama_context * ctx,
+        const std::vector<int32_t> & idxs,
+        const llama_tokens & draft) {
+    GGML_ASSERT(idxs.size() == draft.size() + 1);
+
+    std::vector<llama_token> result;
+    result.reserve(idxs.size());
+
+    for (size_t i = 0; i < draft.size(); ++i) {
+        // the token is discarded - the call is what advances the sampler over this position
+        common_sampler_sample(smpl, ctx, idxs[i]);
+        common_sampler_accept(smpl, draft[i], true);
+        result.push_back(draft[i]);
+    }
+
+    const llama_token id = common_sampler_sample(smpl, ctx, idxs[draft.size()]);
+    common_sampler_accept(smpl, id, true);
+    result.push_back(id);
+
+    return result;
+}
+
 // synthetic draft verification for benchmarking - accept draft tokens at random instead of by match with the target
 // on replay the draft was already accepted before a context checkpoint restore, so repeat the same decisions
 static std::vector<llama_token> server_sample_and_accept_synth(
@@ -212,6 +237,9 @@ struct server_slot {
     common_speculative * spec;
 
     llama_tokens spec_draft;
+
+    // draft candidates per token in spec_draft; only draft-simple and draft-mtp fill it
+    std::vector<std::vector<llama_token_data>> spec_draft_q;
     llama_tokens spec_prompt;
     std::vector<int32_t> spec_i_batch;
     common_prompt_checkpoint spec_ckpt;
@@ -446,6 +474,11 @@ struct server_slot {
         return !!spec;
     }
 
+    // at temp 0 both p and q are point masses, so rejection is the same as sample-and-match
+    bool use_spec_rejection() const {
+        return task && task->params.sampling.temp > 0.0f;
+    }
+
     void add_token(const completion_token_output & token) {
         if (!is_processing()) {
             SLT_WRN(*this, "%s", "slot is not processing\n");
@@ -3088,6 +3121,9 @@ private:
                 if (n_draft_max > 0) {
                     GGML_ASSERT(slot.can_speculate());
 
+                    // stale candidates: a replay never reads them, a new draft refills them
+                    slot.spec_draft_q.clear();
+
                     if (!slot.spec_draft.empty()) {
                         // we have a previous (partial) draft to reuse
                         if (use_ckpt_tgt) {
@@ -3107,6 +3143,8 @@ private:
 
                         slot.spec_prompt = slot.prompt.tokens.get_text_tokens();
 
+                        const bool spec_reject = slot.use_spec_rejection();
+
                         common_speculative_get_draft_params(spec.get(), slot.id) = {
                             /* .drafting = */ true,
                             /* .n_max    = */ n_draft_max,
@@ -3114,6 +3152,9 @@ private:
                             /* .id_last  = */ slot.sampled,
                             /* .prompt   = */ &slot.spec_prompt,
                             /* .result   = */ &slot.spec_draft,
+                            /* .result_q = */ spec_reject ? &slot.spec_draft_q : nullptr,
+                            /* .temp     = */ slot.task->params.sampling.temp,
+                            /* .seed     = */ slot.task->params.sampling.seed,
                         };
 
                         drafting.push_back(&slot);
@@ -4051,12 +4092,25 @@ private:
                 common_sampler_ptr smpl_save(common_sampler_clone(slot.smpl.get()));
 
                 GGML_ASSERT(slot.spec_i_batch.size() == n_draft + 1);
+                GGML_ASSERT(slot.spec_draft_q.empty() || (slot.spec_draft_q.size() == slot.spec_draft.size()));
                 const auto & synth_probs = common_speculative_get_synth_probs(spec.get());
-                auto accepted = synth_probs.empty()
-                    ? common_sampler_sample_and_accept_n(slot.smpl.get(), slot.ctx_tgt, slot.spec_i_batch, slot.spec_draft)
-                    : server_sample_and_accept_synth(
+
+                // drafters that fill no distribution fall back here
+                const bool use_rejection = slot.use_spec_rejection() && !slot.spec_draft_q.empty();
+
+                std::vector<llama_token> accepted;
+                if (!synth_probs.empty()) {
+                    // synthetic acceptance replaces verification entirely, so it comes first
+                    accepted = server_sample_and_accept_synth(
                             slot.smpl.get(), slot.ctx_tgt, slot.spec_i_batch, slot.spec_draft,
                             synth_probs, slot.spec_synth_rng, slot.spec_is_replay);
+                } else if (slot.spec_is_replay && slot.use_spec_rejection()) {
+                    accepted = server_accept_replay(slot.smpl.get(), slot.ctx_tgt, slot.spec_i_batch, slot.spec_draft);
+                } else if (use_rejection) {
+                    accepted = common_sampler_sample_and_accept_n_rejection(slot.smpl.get(), slot.ctx_tgt, slot.spec_i_batch, slot.spec_draft, slot.spec_draft_q);
+                } else {
+                    accepted = common_sampler_sample_and_accept_n(slot.smpl.get(), slot.ctx_tgt, slot.spec_i_batch, slot.spec_draft);
+                }
                 slot.spec_i_batch.clear();
 
                 GGML_ASSERT(accepted.size() >= 1);