Add sparsity (#148513)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/148513
Approved by: https://github.com/danielvegamyhre

benchmarks/transformer/sdpa.py

@@ -80,7 +80,10 @@ class Experiment:
 
 
 def calculate_tflops(
-    config: ExperimentConfig, time_us: float, is_backward: bool = False
+    config: ExperimentConfig,
+    time_us: float,
+    is_backward: bool = False,
+    sparsity: float = 0.0,
 ) -> float:
     """
     Calculate TFLOPS for scaled dot product attention.
@@ -89,6 +92,7 @@ def calculate_tflops(
     - config: The experiment configuration
     - time_us: The execution time in microseconds
     - is_backward: Whether to calculate for backward pass (includes gradient computation)
+    - sparsity: Sparsity factor between 0.0 and 1.0, where 0.0 means no sparsity and 1.0 means fully sparse
 
     Returns:
     - TFLOPS value
@@ -99,6 +103,9 @@ def calculate_tflops(
     N = config.kv_seq_len
     D = config.head_dim
 
+    # Calculate density factor (1.0 - sparsity)
+    density = 1.0 - sparsity
+
     # Forward pass FLOPs
     qk_flops = (
         M * N * D * 2
@@ -110,6 +117,9 @@ def calculate_tflops(
 
     total_flops = B * H * (qk_flops + softmax_flops + av_flops)
 
+    # Apply density factor to account for sparsity
+    total_flops *= density
+
     # For backward pass flash uses 2.5x more flops will use this
     if is_backward:
         total_flops *= 2.5
@@ -168,8 +178,11 @@ def run_single_experiment(config: ExperimentConfig) -> ExperimentResults:
         )
 
     # Calculate TFLOPS for forward and backward passes
-    forward_tflops = calculate_tflops(config, forward_time)
-    backward_tflops = calculate_tflops(config, backward_time, is_backward=True)
+    sparsity = 0.5 if is_causal else 0.0
+    forward_tflops = calculate_tflops(config, forward_time, sparsity=sparsity)
+    backward_tflops = calculate_tflops(
+        config, backward_time, is_backward=True, sparsity=sparsity
+    )
 
     return ExperimentResults(
         forward_time=forward_time,