Add input padding during prefill for qwen2-7b (#12033)

python/llm/src/ipex_llm/transformers/npu_models/qwen2_mp.py

@@ -934,8 +934,21 @@ def forward(
                 " to max_prompt_len {self.max_prompt_len}"
             ),
         )
-        self.prefill_input_queue.put((hidden_states, position_ids, attention_mask, past_key_value))
-        return self.prefill_result_queue.get()
+        pad_len = self.max_prompt_len - seq_len
+        hidden_states = F.pad(hidden_states.to(torch.float16), (0, 0, 0, pad_len), value=0.0)
+        position_ids = F.pad(position_ids, (0, pad_len), value=0)
+        attention_mask = F.pad(
+            attention_mask.to(torch.float16),
+            (0, pad_len, 0, pad_len),
+            value=torch.finfo(torch.float16).min,
+        )
+
+        args = (hidden_states, position_ids, attention_mask, past_key_value)
+        self.prefill_input_queue.put(args)
+        hidden_states, past_key_value = self.prefill_result_queue.get()
+        past_key_value.shrink(seq_len, self.transpose_value_cache)
+        hidden_states = hidden_states[:, :seq_len, :]
+        return hidden_states, past_key_value
 
     def shutdown(self):
         self.prefill_input_queue.put("stop")