spec: add spec metrics mean acceptance length and acceptance rate per position (#24536)

* spec: add spec metrics mean acceptance length and acceptance per pos

* fix as suggestion

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

* fix as suggestion

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

* fix as suggestion

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

* fix as suggestions

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

common/speculative.cpp

@@ -140,6 +140,8 @@ struct common_speculative_impl {
     size_t n_gen_tokens = 0; // number of tokens generated by this implementation.
     size_t n_acc_tokens = 0; // number of tokens accepted by the target model.
 
+    std::vector<size_t> n_acc_tokens_per_pos; // number of tokens accepted per draft position.
+
     // TODO: track performance of most recent calls
     const bool gen_perf = true; // whether to generate performance stats.
 
@@ -2059,6 +2061,15 @@ void common_speculative_accept(common_speculative * spec, llama_seq_id seq_id, u
 
     {
         common_time_meas tm(impl->t_accept_us, !impl->gen_perf);
+
+        if (impl->n_acc_tokens_per_pos.size() < n_accepted) {
+            impl->n_acc_tokens_per_pos.resize(n_accepted, 0);
+        }
+
+        for (size_t i = 0; i < n_accepted; ++i) {
+            impl->n_acc_tokens_per_pos[i]++;
+        }
+
         if (n_accepted > 0) {
             impl->n_acc_drafts++;
             impl->n_acc_tokens += n_accepted;
@@ -2093,13 +2104,31 @@ void common_speculative_print_stats(const common_speculative * spec) {
             str_perf = "";
         }
 
-        LOG_INF("statistics %16s: #calls(b,g,a) = %4zu %6zu %6zu, #gen drafts = %6zu, #acc drafts = %5zu, #gen tokens = %6zu, #acc tokens = %5zu%s\n",
+        std::string str_stats;
+        if (impl->n_call_accept > 0) {
+            const double mean =
+                1.0 + (double) impl->n_acc_tokens / (double) impl->n_call_accept;
+            std::ostringstream tmp;
+            tmp << std::fixed << std::setprecision(3);
+            for (size_t i = 0; i < impl->n_acc_tokens_per_pos.size(); ++i) {
+                if (i > 0) {
+                    tmp << ", ";
+                }
+                tmp << (double) impl->n_acc_tokens_per_pos[i] / (double) impl->n_call_accept;
+            }
+            std::ostringstream oss;
+            oss << std::fixed << std::setprecision(2) << mean;
+            str_stats = ", #mean acc len = " + oss.str() + ", #acc rate/pos = (" + tmp.str() + ")";
+        }
+
+        LOG_INF("statistics %16s: #calls(b,g,a) = %4zu %6zu %6zu, #gen drafts = %6zu, #acc drafts = %5zu, #gen tokens = %6zu, #acc tokens = %5zu%s%s\n",
                 common_speculative_type_to_str(impl->type).c_str(),
                 impl->n_call_begin, impl->n_call_draft, impl->n_call_accept,
                 impl->n_gen_drafts,
                 impl->n_acc_drafts,
                 impl->n_gen_tokens,
                 impl->n_acc_tokens,
+                str_stats.c_str(),
                 str_perf.c_str());
     }
 }

tools/server/server-context.cpp

@@ -201,6 +201,8 @@ struct server_slot {
     // Speculative decoding stats
     int32_t n_draft_total = 0;      // Total draft tokens generated
     int32_t n_draft_accepted = 0;   // Draft tokens actually accepted
+    int32_t n_draft_verif_steps = 0; // Total draft token verification steps by the target model
+    std::vector<int32_t> n_accepted_per_pos; // Accepted tokens per draft position
 
     void reset() {
         SLT_DBG(*this, "%s", "\n");
@@ -227,6 +229,8 @@ struct server_slot {
         // clear speculative decoding stats
         n_draft_total = 0;
         n_draft_accepted = 0;
+        n_draft_verif_steps = 0;
+        n_accepted_per_pos.clear();
 
         task_prev = std::move(task);
         task.reset();
@@ -509,10 +513,22 @@ struct server_slot {
                 llama_perf_context(ctx_tgt).n_reused);
 
         if (n_draft_total > 0) {
-            const float draft_ratio = (float) n_draft_accepted / n_draft_total;
+            const float  draft_ratio  = (float) n_draft_accepted / n_draft_total;
+            const double mean_acc_len = n_draft_verif_steps > 0 ? 1.0 + (double) n_draft_accepted / (double) n_draft_verif_steps : 1.0;
+
+            std::string acceptance_rates_per_pos;
+            if (n_draft_verif_steps > 0) {
+                for (size_t i = 0; i < n_accepted_per_pos.size(); ++i) {
+                    if (i > 0) {
+                        acceptance_rates_per_pos += ", ";
+                    }
+                    acceptance_rates_per_pos += string_format("%.3f", (double) n_accepted_per_pos[i] / (double) n_draft_verif_steps);
+                }
+            }
+
             SLT_INF(*this,
-                    "draft acceptance = %0.5f (%5d accepted / %5d generated)\n",
+                    "draft acceptance = %0.5f (%5d accepted / %5d generated), mean acceptance length = %5.2f, acceptance rate per position = (%s)\n",
-                    draft_ratio, n_draft_accepted, n_draft_total);
+                    draft_ratio, n_draft_accepted, n_draft_total, mean_acc_len, acceptance_rates_per_pos.c_str());
         }
 
         common_speculative_print_stats(spec);
@@ -3543,6 +3559,14 @@ private:
 
                 // update how many tokens out of those tested were accepted
                 slot.n_draft_accepted += ids.size() - 1;
+                slot.n_draft_verif_steps += 1;
+
+                if (slot.n_accepted_per_pos.empty()) {
+                    slot.n_accepted_per_pos.resize(common_speculative_n_max(&params_base.speculative), 0);
+                }
+                for (size_t i = 0; i < ids.size() - 1 && i < slot.n_accepted_per_pos.size(); ++i) {
+                    slot.n_accepted_per_pos[i]++;
+                }
 
                 // add accepted tokens to the prompt
                 slot.prompt.tokens.keep_first(slot.prompt.n_tokens() - n_draft);