server : reuse context chunks

ggml-ci

Author: ggerganov

examples/server/server.cpp

@@ -800,7 +800,7 @@ struct server_context {
                 int slot_prompt_len = slot_prompt.size();
 
                 // length of the Longest Common Prefix between the current slot's prompt and the input prompt
-                int lcp_len = common_part(slot_prompt, prompt);
+                int lcp_len = longest_common_prefix(slot_prompt, prompt);
 
                 // fraction of the common substring length compared to the current slot's prompt length
                 similarity = static_cast<float>(lcp_len) / slot_prompt_len;
@@ -2042,12 +2042,61 @@ struct server_context {
 
                             if (slot.params.cache_prompt) {
                                 // reuse any previously computed tokens that are common with the new prompt
-                                slot.n_past = common_part(slot.cache_tokens, prompt_tokens);
+                                slot.n_past = longest_common_prefix(slot.cache_tokens, prompt_tokens);
 
                                 // push the prompt into the sampling context (do not apply grammar)
                                 for (int i = 0; i < slot.n_past; ++i) {
                                     common_sampler_accept(slot.smpl, slot.cache_tokens[i], false);
                                 }
+
+                                // EXPERIMENTAL: reuse chunks from the cached prompt by shifting them in the new position
+                                if (1) {
+                                    size_t head_c = slot.n_past; // cache
+                                    size_t head_p = slot.n_past; // current prompt
+
+                                    while (head_c < slot.cache_tokens.size() &&
+                                           head_p < prompt_tokens.size() &&
+                                           !llama_token_is_control(model, slot.cache_tokens[head_c]) &&
+                                           !llama_token_is_control(model, prompt_tokens[head_p])) {
+
+                                        size_t n_match = 0;
+                                        while (head_c + n_match < slot.cache_tokens.size() &&
+                                               head_p + n_match < prompt_tokens.size()     &&
+                                               !llama_token_is_control(model, slot.cache_tokens[head_c + n_match]) &&
+                                               !llama_token_is_control(model, prompt_tokens[head_p + n_match]) &&
+                                               slot.cache_tokens[head_c + n_match] == prompt_tokens[head_p + n_match]) {
+                                            n_match++;
+                                        }
+
+                                        if (n_match > 32) {
+                                            // shift the KV chunk [head_c, head_c + n_match) -> [head_p, head_p + n_match)
+                                            SLT_DBG(slot, "shifting KV cache [%zu, %zu) -> [%zu, %zu)\n", head_c, head_c + n_match, head_p, head_p + n_match);
+                                            //for (size_t i = head_p; i < head_p + n_match; i++) {
+                                            //    SLT_DBG(slot, "cache token %3zu: %6d '%s'\n", i, prompt_tokens[i], common_token_to_piece(ctx, prompt_tokens[i]).c_str());
+                                            //}
+
+                                            const int64_t kv_shift = (int64_t) head_p - (int64_t) head_c;
+
+                                            llama_kv_cache_seq_rm (ctx, slot.id + 1, head_p, head_c);
+                                            llama_kv_cache_seq_add(ctx, slot.id + 1, head_c, -1,     kv_shift);
+
+                                            for (size_t i = 0; i < n_match; i++) {
+                                                slot.cache_tokens[head_p + i] = slot.cache_tokens[head_c + i];
+
+                                                common_sampler_accept(slot.smpl, slot.cache_tokens[head_p + i], false);
+
+                                                slot.n_past++;
+                                            }
+
+                                            head_c += n_match;
+                                            head_p += n_match;
+                                        } else {
+                                            head_c += 1;
+                                        }
+                                    }
+
+                                    SLT_DBG(slot, "new slot.n_past = %d, cache_tokens.size() = %zu\n", slot.n_past, slot.cache_tokens.size());
+                                }
                             }
                         }
 
@@ -3257,6 +3306,7 @@ int main(int argc, char ** argv) {
 
     ctx_server.queue_tasks.on_new_task(std::bind(
                 &server_context::process_single_task, &ctx_server, std::placeholders::_1));
+
     ctx_server.queue_tasks.on_update_slots(std::bind(
                 &server_context::update_slots, &ctx_server));
 

examples/server/utils.hpp

@@ -195,14 +195,14 @@ static std::string gen_chatcmplid() {
 // other common utils
 //
 
-static size_t common_part(const std::vector<llama_token> & a, const std::vector<llama_token> & b) {
+static size_t longest_common_prefix(const std::vector<llama_token> & a, const std::vector<llama_token> & b) {
     size_t i;
     for (i = 0; i < a.size() && i < b.size() && a[i] == b[i]; i++) {}
 
     return i;
 }
 
-static size_t common_part(const std::string & a, const std::string & b) {
+static size_t longest_common_prefix(const std::string & a, const std::string & b) {
     size_t i;
     for (i = 0; i < a.size() && i < b.size() && a[i] == b[i]; i++) {}