Memory optimization for gpt_bitcode (#4) (huggingface#1513)

Co-authored-by: Urszula Golowicz <urszula.golowicz@intel.com>

optimum/habana/transformers/models/gpt_bigcode/modeling_gpt_bigcode.py

@@ -24,7 +24,12 @@
 import torch.utils.checkpoint
 from torch.nn import CrossEntropyLoss
 from transformers.modeling_outputs import BaseModelOutputWithPastAndCrossAttentions, CausalLMOutputWithCrossAttentions
-from transformers.models.gpt_bigcode.modeling_gpt_bigcode import GPTBigCodeAttention, GPTBigCodeForCausalLM
+from transformers.models.gpt_bigcode.modeling_gpt_bigcode import (
+    GPTBigCodeAttention,
+    GPTBigCodeForCausalLM,
+    upcast_masked_softmax,
+    upcast_softmax,
+)
 
 from ...modeling_attn_mask_utils import GaudiAttentionMaskConverter
 
@@ -57,6 +62,90 @@ def __init__(self, config, is_cross_attention=False, layer_idx=None):
         self.fused_scaled_dot_product_attention = ModuleFusedSDPA(FusedSDPA) if FusedSDPA is not None else None
         self.block_size = 4096
 
+    def _attn(self, query, key, value, attention_mask=None, head_mask=None):
+        """
+        This method should be deleted when https://github.com/huggingface/transformers/pull/34508 is merged.
+        Copied from GPTBigCodeAttention._attn: https://github.com/huggingface/transformers/blob/v4.40-release/src/transformers/models/gpt_bigcode/modeling_gpt_bigcode.py
+        The only differences are:
+        - in self._attn, use torch.matmul instead of torch.baddbmm when the device used for query is not cpu
+        """
+        dtype = query.dtype
+        softmax_dtype = torch.float32 if self.attention_softmax_in_fp32 else dtype
+        upcast = dtype != softmax_dtype
+
+        unscale = self.layer_idx + 1 if self.scale_attention_softmax_in_fp32 and upcast else 1
+        scale_factor = unscale**-1
+        if self.scale_attn_weights:
+            scale_factor /= self.head_dim**0.5
+
+        # MQA models: (batch_size, query_length, num_heads * head_dim)
+        # MHA models: (batch_size, num_heads, query_length, head_dim)
+        query_shape = query.shape
+        batch_size = query_shape[0]
+        key_length = key.size(-1)
+        if self.multi_query:
+            # (batch_size, query_length, num_heads, head_dim) x (batch_size, head_dim, key_length)
+            # -> (batch_size, query_length, num_heads, key_length)
+            query_length = query_shape[1]
+            attn_shape = (batch_size, query_length, self.num_heads, key_length)
+            attn_view = (batch_size, query_length * self.num_heads, key_length)
+            # No copy needed for MQA 2, or when layer_past is provided.
+            query = query.reshape(batch_size, query_length * self.num_heads, self.head_dim)
+        else:
+            # (batch_size, num_heads, query_length, head_dim) x (batch_size, num_heads, head_dim, key_length)
+            # -> (batch_size, num_heads, query_length, key_length)
+            query_length = query_shape[2]
+            attn_shape = (batch_size, self.num_heads, query_length, key_length)
+            attn_view = (batch_size * self.num_heads, query_length, key_length)
+            # Always copies
+            query = query.reshape(batch_size * self.num_heads, query_length, self.head_dim)
+            # No copy when layer_past is provided.
+            key = key.reshape(batch_size * self.num_heads, self.head_dim, key_length)
+
+        attn_weights = torch.empty(attn_view, device=query.device, dtype=query.dtype)
+        if query.device.type == "cpu":
+            # This is needed because of a bug in pytorch https://github.com/pytorch/pytorch/issues/80588.
+            # The bug was fixed in https://github.com/pytorch/pytorch/pull/96086,
+            # but the fix has not been released as of pytorch version 2.0.0.
+            attn_weights = torch.zeros_like(attn_weights)
+            attn_weights = torch.baddbmm(attn_weights, query, key, beta=1, alpha=scale_factor).view(attn_shape)
+        else:
+            # Formula for torch.baddbmm: out = beta * attn_weights + scale_factor * (query ⋅ key)
+            # for beta = 0, it simplifies to: out = scale_factor * (query ⋅ key)
+            attn_weights = (torch.matmul(query, key) * scale_factor).view(attn_shape)
+
+        if upcast:
+            # Use a fused kernel to prevent a large overhead from casting and scaling.
+            # Sub-optimal when the key length is not a multiple of 8.
+            if attention_mask is None:
+                attn_weights = upcast_softmax(attn_weights, unscale, softmax_dtype)
+            else:
+                mask_value = self._get_mask_value(attn_weights.device, softmax_dtype)
+                attn_weights = upcast_masked_softmax(attn_weights, attention_mask, mask_value, unscale, softmax_dtype)
+        else:
+            if attention_mask is not None:
+                mask_value = self._get_mask_value(attn_weights.device, softmax_dtype)
+
+                # The fused kernel is very slow when the key length is not a multiple of 8, so we skip fusion.
+                attn_weights = torch.where(attention_mask, attn_weights, mask_value)
+
+            attn_weights = torch.nn.functional.softmax(attn_weights, dim=-1)
+
+        attn_weights = self.attn_dropout(attn_weights)
+
+        # Mask heads if we want to
+        if head_mask is not None:
+            if self.multi_query:
+                head_mask = head_mask.transpose(1, 2)
+            attn_weights = attn_weights * head_mask
+
+        if self.multi_query:
+            attn_output = torch.bmm(attn_weights.view(attn_view), value).view(query_shape)
+        else:
+            attn_output = torch.matmul(attn_weights, value)
+
+        return attn_output, attn_weights
+
     def gaudi_flash_attn_v1(
         self,
         query_layer,