fix: incomplete generations w/ single tokens generations and models that did...

fix: incomplete generations w/ single tokens generations and models that did not support chunking (#2770)

* Incomplete generation stream fix (#2754)

entries.len() could > batch.size in prefill, so need to filter as well.
Signed-off-by: Wang, Yi A <yi.a.wang@intel.com>

* entries was wrongly extended for model that did not support chunking

---------
Signed-off-by: Wang, Yi A <yi.a.wang@intel.com>
Co-authored-by: Wang, Yi <yi.a.wang@intel.com>

backends/v3/src/backend.rs

@@ -193,7 +193,7 @@ pub(crate) async fn batching_task(
                 };
 
                 // Try to get a new batch
-                if let Some((new_entries, new_batch, span)) = queue
+                if let Some((mut new_entries, new_batch, span)) = queue
                     .next_batch(min_size, max_size, prefill_token_budget, token_budget)
                     .await
                 {
@@ -209,11 +209,26 @@ pub(crate) async fn batching_task(
                         };
                         counter.increment(1);
                     }
-                    let cached_batch = if support_chunking {
-                        // Concat current batch to the new one
-                        batches.pop()
+
+                    let new_cached_batch = if support_chunking {
+                        // Get cached batch
+                        let cached_batch = batches.pop();
+                        // Extend entries with the new entries since the batch will be
+                        // concatenated during the prefill op server side
+                        entries.extend(new_entries);
+                        // Generate one token for both the cached batch and the new batch
+                        let new_cached_batch =
+                            prefill(&mut client, new_batch, cached_batch, &mut entries)
+                                .instrument(span)
+                                .await;
+                        if new_cached_batch.is_none() {
+                            // New cached batch is empty, no work left
+                            break;
+                        }
+                        new_cached_batch
                     } else {
-                        // Request are waiting only if we don't support chunking
+                        // Request are waiting because we cannot concatenate the batches if the
+                        // model/server does not support chunking
                         entries.iter_mut().for_each(|(_, entry)| {
                             // Create a new span to add the info that this entry is waiting
                             // because a new batch is being computed
@@ -224,23 +239,24 @@ pub(crate) async fn batching_task(
                             // Update entry
                             entry.temp_span = Some(entry_waiting_span);
                         });
-                        None
-                    };
-                    entries.extend(new_entries);
 
                         // Generate one token for this new batch to have the attention past in cache
                         let new_cached_batch =
-                        prefill(&mut client, new_batch, cached_batch, &mut entries)
+                            prefill(&mut client, new_batch, None, &mut new_entries)
                                 .instrument(span)
                                 .await;
+                        if new_cached_batch.is_some() {
+                            // Extend entries
+                            entries.extend(new_entries);
+                        }
+                        new_cached_batch
+                    };
+
                     // Reset waiting counter
                     waiting_tokens = 1;
                     // Extend current batch with the new batch
                     if let Some(new_cached_batch) = new_cached_batch {
                         batches.push(new_cached_batch);
-                    } else if support_chunking {
-                        // New cached batch is empty, no work left
-                        break;
                     }
                 }