diff --git a/vllm/envs.py b/vllm/envs.py
index ab12a7b48dc53..be5d9985b63a4 100644
--- a/vllm/envs.py
+++ b/vllm/envs.py
@@ -69,6 +69,7 @@
     VLLM_DISABLED_KERNELS: List[str] = []
     VLLM_USE_V1: bool = False
     VLLM_ENABLE_V1_MULTIPROCESSING: bool = False
+    VLLM_LOG_BATCHSIZE_INTERVAL: float = -1
 
 
 def get_default_cache_root():
@@ -452,6 +453,8 @@ def get_default_config_root():
     # If set, enable multiprocessing in LLM for the V1 code path.
     "VLLM_ENABLE_V1_MULTIPROCESSING":
     lambda: bool(int(os.getenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0"))),
+    "VLLM_LOG_BATCHSIZE_INTERVAL":
+    lambda: float(os.getenv("VLLM_LOG_BATCHSIZE_INTERVAL", "-1")),
 }
 
 # end-env-vars-definition
diff --git a/vllm/forward_context.py b/vllm/forward_context.py
index aaa3e4bb3a1e8..cd136f43c0c57 100644
--- a/vllm/forward_context.py
+++ b/vllm/forward_context.py
@@ -1,8 +1,19 @@
+import time
+from collections import Counter
 from contextlib import contextmanager
 from dataclasses import dataclass
 from typing import Any, Dict, Optional
 
+import vllm.envs as envs
 from vllm.config import VllmConfig
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
+
+track_batchsize: bool = envs.VLLM_LOG_BATCHSIZE_INTERVAL >= 0
+batchsize_counter: Counter = Counter()
+last_logging_time: float = 0
+batchsize_logging_interval: float = envs.VLLM_LOG_BATCHSIZE_INTERVAL
 
 
 @dataclass
@@ -26,7 +37,26 @@ def get_forward_context() -> ForwardContext:
 @contextmanager
 def set_forward_context(context: Any, vllm_config: VllmConfig):
     """A context manager that stores the current forward context,
-    can be attention metadata, etc."""
+    can be attention metadata, etc.
+    Here we can inject common logic for every model forward pass.
+    """
+    global track_batchsize, batchsize_counter
+    global last_logging_time, batchsize_logging_interval
+    if track_batchsize and context is not None:
+        if hasattr(context, "num_prefill_tokens"):
+            # for v0 attention backends
+            batchsize = context.num_prefill_tokens + context.num_decode_tokens
+        else:
+            # for v1 attention backends
+            batchsize = context.num_input_tokens
+        batchsize_counter[batchsize] += 1
+        if time.monotonic() - last_logging_time > batchsize_logging_interval:
+            last_logging_time = time.monotonic()
+            sorted_data = sorted(batchsize_counter.items(),
+                                 key=lambda x: x[1],
+                                 reverse=True)
+            logger.info("Batchsize distribution (batchsize, count): %s",
+                        sorted_data)
     global _forward_context
     prev_context = _forward_context
     _forward_context = ForwardContext(
diff --git a/vllm/v1/attention/backends/flash_attn.py b/vllm/v1/attention/backends/flash_attn.py
index 251a103e60f06..c9f04ace644c7 100644
--- a/vllm/v1/attention/backends/flash_attn.py
+++ b/vllm/v1/attention/backends/flash_attn.py
@@ -56,6 +56,7 @@ class FlashAttentionMetadata:
     seq_start_loc: torch.Tensor
     block_table: torch.Tensor
     slot_mapping: torch.Tensor
+    num_input_tokens: int = 0  # Number of tokens including padding.
 
 
 class FlashAttentionImpl(AttentionImpl):
diff --git a/vllm/v1/worker/gpu_model_runner.py b/vllm/v1/worker/gpu_model_runner.py
index 0a5adfb28c9bd..a3335fa838352 100644
--- a/vllm/v1/worker/gpu_model_runner.py
+++ b/vllm/v1/worker/gpu_model_runner.py
@@ -445,6 +445,8 @@ def execute_model(
             # Eager mode.
             num_input_tokens = num_scheduled_tokens
 
+        attn_metadata.num_input_tokens = num_input_tokens
+
         # Get the inputs embeds.
         if encoder_outputs:
             inputs_embeds = self.model.get_input_embeddings(