Add MLP/lm_head tp grain size setting. (#6828)

This PR aims to add MLP/lm_head tp size granularity setting to
deepspeed.init_inference() API. It will be more flexible to set the
MLP/lm_head sharding grain size.

DNN library favors tensor size in granularity of power of 2, we pick 64
as a default size.

We aim to be able to set the MLP/lm_head tp grain size flexibly. This is
a preliminary solution. If there is a better solution, we can discuss it
together. Thanks~

---------

Co-authored-by: Logan Adams <[email protected]>
Co-authored-by: Olatunji Ruwase <[email protected]>

Author: 3 people

deepspeed/inference/config.py

@@ -40,6 +40,9 @@ class DeepSpeedTPConfig(DeepSpeedConfigModel):
     tp_size: int = 1
     """ Number of devices to split the model across using tensor parallelism. """
 
+    tp_grain_size: int = 64
+    "Desired MLP/lm_head tp size granularity. DNN library favors tensor size in granularity of power of 2, we pick 64 as a default size."
+
     mpu: object = None
     """
     A model parallelism unit object that implements

deepspeed/module_inject/replace_module.py

@@ -17,7 +17,7 @@
 from .layers import TensorParallelOcShardConv2d, TensorParallelIcShardConv2d
 
 from deepspeed import comm as dist
-from deepspeed.module_inject.tp_shard import set_num_kv_heads, set_n_embd, set_num_attention_heads
+from deepspeed.module_inject.tp_shard import set_num_kv_heads, set_n_embd, set_num_attention_heads, set_tp_grain_size
 
 from .load_checkpoint import load_model_with_checkpoint
 import time
@@ -303,6 +303,9 @@ def replace_wo_policy(module, all_reduce_linears, prefix="", state_dict=None):
         if hasattr(model_config, 'num_attention_heads'):
             set_num_attention_heads(getattr(model_config, 'num_attention_heads'))
 
+        # 4.4 set tp_grain_size
+        set_tp_grain_size(config.tensor_parallel.tp_grain_size)
+
         # 5. Set linear policies
         _autotp.update_linear_policies()
 

deepspeed/module_inject/tp_shard.py

@@ -22,6 +22,11 @@ def set_n_embd(num):
     n_embd = num
 
 
+def set_tp_grain_size(num):
+    global tp_grain_size
+    tp_grain_size = num
+
+
 def get_num_kv_heads():
     global num_kv_heads
     if 'num_kv_heads' in globals():
@@ -45,9 +50,9 @@ def get_shard_size(total_size, mp_size, name=None, rank=None):
         my_slices = (num_kv_heads // mp_size) + (1 if rank < (num_kv_heads % mp_size) else 0)
         return total_size * my_slices // num_kv_heads
     else:
-        if total_size >= 64:
-            grain_size = total_size // 64
-            return (grain_size // mp_size + (1 if rank < (grain_size % mp_size) else 0)) * 64
+        if total_size >= tp_grain_size:
+            grain_size = total_size // tp_grain_size
+            return (grain_size // mp_size + (1 if rank < (grain_size % mp_size) else 0)) * tp_grain_size
         else:
             return total_size // mp_size + (1 if rank < (total_size % mp_size) else 0)