Optimize the performance of FlashBert Path for HPU (#575)

Signed-off-by: Liu, Kaixuan <kaixuan.liu@intel.com>

Author: kaixuanliu

backends/python/server/text_embeddings_server/models/flash_bert.py

@@ -323,19 +323,21 @@ def batch_type(self) -> Union[FlashBatch, PaddedBatch]:
     def embed(self, batch: Union[FlashBatch, PaddedBatch]) -> List[Embedding]:
         if isinstance(batch, PaddedBatch):
             input_lens = batch.attention_mask.cumsum(-1)[:, -1].to(torch.int32)
-            max_input_lens = input_lens.max().item()
+            max_input_lens = 0  # This value will not be used
             cu_seqlens = torch.cat(
                 (input_lens.new_tensor([0]), input_lens.cumsum(-1).int())
             )
             mask = batch.attention_mask.bool()
-            batch_size = input_lens.size(0)
+            bsz, tgt_len = mask.size()
+            min_val = torch.finfo(self.dtype).min
             attn_mask = torch.full(
-                [batch_size, 1, 1, mask.shape[-1]],
-                fill_value=torch.finfo(self.dtype).min,
+                [bsz, 1, tgt_len, tgt_len],
+                fill_value=min_val,
                 device=self.device,
                 dtype=self.dtype,
             )
-            attn_mask.masked_fill_(mask[:, None, None, :], 0)
+            expanded_mask = mask[:, None, None, :].expand(bsz, 1, tgt_len, tgt_len)
+            attn_mask = attn_mask.masked_fill(expanded_mask, 0.0)
         elif isinstance(batch, FlashBatch):
             cu_seqlens = batch.cu_seqlens
             mask = None