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server : chunked prefill support #10718

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server : chunked prefill support #10718

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26 changes: 25 additions & 1 deletion examples/server/server.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2418,6 +2418,14 @@ struct server_context {
int32_t n_batch = llama_n_batch(ctx);
int32_t n_ubatch = llama_n_ubatch(ctx);

// there are currently slots with ongoing text generation
const bool is_tg = batch.n_tokens > 0;

// limit the batch to avoid blocking the processing
if (is_tg) {
n_batch = 32; // TODO: configurable
}

// track if this is an embedding or non-embedding batch
// if we've added sampled tokens above, we are in non-embedding mode
// -1: none, 0: non-embedding, 1: embedding
Expand All @@ -2426,6 +2434,18 @@ struct server_context {

// next, batch any pending prompts without exceeding n_batch
if (params_base.cont_batching || batch.n_tokens == 0) {
// count how many slots are currently processing prompt
int n_slots_pp = 0;
for (auto & slot : slots) {
if (slot.state == SLOT_STATE_PROCESSING_PROMPT || slot.state == SLOT_STATE_STARTED) {
n_slots_pp++;
}
}

// determine the chunk size of the chunk prefill
// a slot cannot submit more than this number of tokens in a single batch if other slots are processing
const int32_t n_chunk_pp = std::max(n_slots_pp > 0 ? (n_batch / n_slots_pp) : n_batch, 8);

for (auto & slot : slots) {
// this slot still has a prompt to be processed
if (slot.state == SLOT_STATE_PROCESSING_PROMPT || slot.state == SLOT_STATE_STARTED) {
Expand Down Expand Up @@ -2609,8 +2629,10 @@ struct server_context {
// remove the non-common part from the cache
slot.cache_tokens.resize(slot.n_past);

int n_cur = 0;

// add prompt tokens for processing in the current batch
while (slot.n_past < slot.n_prompt_tokens && batch.n_tokens < n_batch) {
while (slot.n_past < slot.n_prompt_tokens && batch.n_tokens < n_batch && n_cur < n_chunk_pp) {
common_batch_add(batch, prompt_tokens[slot.n_past], slot.n_past, { slot.id }, false);

if (slot.params.cache_prompt) {
Expand All @@ -2619,6 +2641,8 @@ struct server_context {

slot.n_prompt_tokens_processed++;
slot.n_past++;

n_cur++;
}

SLT_INF(slot, "prompt processing progress, n_past = %d, n_tokens = %d, progress = %f\n", slot.n_past, batch.n_tokens, (float) slot.n_prompt_tokens_processed / slot.n_prompt_tokens);
Expand Down
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