diff --git a/cacheflow/master/scheduler.py b/cacheflow/master/scheduler.py
index 2ca10117..3d2e300a 100644
--- a/cacheflow/master/scheduler.py
+++ b/cacheflow/master/scheduler.py
@@ -10,10 +10,17 @@ class Scheduler:
 
     def __int__(
         self,
+        controllers: List,
         block_size: int,
         num_gpu_blocks: int,
         num_cpu_blocks: int,
     ) -> None:
+        self.controllers = controllers
+        self.block_size = block_size
+        self.num_gpu_blocks = num_gpu_blocks
+        self.num_cpu_blocks = num_cpu_blocks
+
+        # Create the block space manager.
         self.block_manager = BlockSpaceManager(
             block_size=block_size,
             num_gpu_blocks=num_gpu_blocks,
@@ -31,9 +38,13 @@ class Scheduler:
 
         # Swapped sequence groups (LIFO).
         self.swapped: List[SequenceGroup] = []
-
         # Pending sequence groups (FIFO).
-        self.queue: List[SequenceGroup] = []
+        self.pending: List[SequenceGroup] = []
+
+        # Blocks that need to be swaped or copied before model execution.
+        self.blocks_to_swap_in: Dict[int, int] = []
+        self.blocks_to_swap_out: Dict[int, int] = []
+        self.blocks_to_copy: Dict[int, int] = []
 
     def _free_seq(self, seq: Sequence) -> None:
         seq.status = SequenceStatus.FINISHED
@@ -52,12 +63,11 @@ class Scheduler:
             ret = self.block_manager.append(seq)
             if ret is not None:
                 src_block, dst_block = ret
-                # TODO: Issue COPY commands to the workers.
+                self.blocks_to_copy[src_block] = dst_block
 
     def _swap_in(self, seq_group: SequenceGroup) -> None:
-        # TODO: Issue SWAP_IN commands to the workers.
-        self.block_manager.swap_in(seq_group)
-        self.block_manager.append(seq_group)
+        mapping = self.block_manager.swap_in(seq_group)
+        self.blocks_to_swap_in.update(mapping)
         for seq in seq_group.seqs:
             if seq.status == SequenceStatus.SWAPPED:
                 seq.status = SequenceStatus.RUNNING
@@ -65,14 +75,14 @@ class Scheduler:
 
     def _swap_out(self, seq_group: SequenceGroup) -> None:
         assert self.block_manager.can_swap_out(seq_group)
-        # TODO: Issue SWAP_OUT commands to the workers.
-        self.block_manager.swap_out(seq_group)
+        mapping = self.block_manager.swap_out(seq_group)
+        self.blocks_to_swap_out.update(mapping)
         for seq in seq_group.seqs:
             if seq.status == SequenceStatus.RUNNING:
                 seq.status = SequenceStatus.SWAPPED
         self.swapped.append(seq_group)
 
-    def step(self) -> None:
+    def prepare(self) -> None:
         # 1. Prepare new slots for the running sequences.
         # NOTE: Here we implicitly assume FCFS scheduling.
         # That is, the most recently added sequence group is the first
@@ -100,6 +110,7 @@ class Scheduler:
         for i, seq_group in enumerate(reversed(self.swapped)):
             if self.block_manager.can_swap_in(seq_group):
                 self._swap_in(seq_group)
+                self._append(seq_group)
             else:
                 # OOM. Stop swapping.
                 self.swapped = self.swapped[:len(self.swapped) - i]
@@ -112,14 +123,30 @@ class Scheduler:
         # NOTE: Here we implicitly assume FCFS scheduling.
         # TODO(woosuk): Add a heuristic to control the maximum batch size.
         if not self.swapped:
-            for i, seq_group in enumerate(self.queue):
+            for i, seq_group in enumerate(self.pending):
                 if self.block_manager.can_allocate(seq_group):
                     self._allocate(seq_group)
                 else:
                     # FIXME: Consider the race condition.
-                    self.queue = self.queue[i:]
+                    self.pending = self.pending[i:]
                     break
 
+    def step(self) -> None:
+        # Ensure that either swap-in or swap-out is performed.
+        if self.blocks_to_swap_in is not None:
+            assert self.blocks_to_swap_out is None
+
+        # Execute the first stage of the pipeline.
+        self.controllers[0].execute_stage(
+            self.blocks_to_swap_in.copy(),
+            self.blocks_to_swap_out.copy(),
+            self.blocks_to_copy.copy(),
+        )
+        # Clear for the next step.
+        self.blocks_to_swap_in.clear()
+        self.blocks_to_swap_out.clear()
+        self.blocks_to_copy.clear()
+
     def post_step(
         self,
         next_tokens: Dict[int, Tuple[int, int]],