[Fix] Reduce busy polling when scheduler is idle (#6026)

docs/backend/server_arguments.md

@@ -107,7 +107,7 @@ Please consult the documentation below and [server_args.py](https://github.com/s
 | `--download-dir` | Model download directory for huggingface. | None |
 | `--base-gpu-id` | The base GPU ID to start allocating GPUs from. Useful when running multiple instances on the same machine. | 0 |
 | `--gpu-id-step` | The delta between consecutive GPU IDs that are used. For example, setting it to 2 will use GPU 0,2,4,.... | 1 |
-
+| `--sleep-on-idle` | Reduce CPU usage when sglang is idle. | False |
 
 ## Logging
 

python/sglang/srt/disaggregation/decode.py

@@ -550,6 +550,7 @@ class SchedulerDisaggregationDecodeMixin:
                 # When the server is idle, do self-check and re-init some states
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
 
@@ -628,6 +629,7 @@ class SchedulerDisaggregationDecodeMixin:
                 # When the server is idle, do self-check and re-init some states
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
             self.last_batch_in_queue = last_batch_in_queue

python/sglang/srt/disaggregation/prefill.py

@@ -242,6 +242,7 @@ class SchedulerDisaggregationPrefillMixin:
             if batch is None and len(self.disagg_prefill_inflight_queue) == 0:
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
             # HACK (byronhsu): reset the batch_is_full flag because we never enter update_running_batch which resets it
@@ -294,6 +295,7 @@ class SchedulerDisaggregationPrefillMixin:
             if batch is None and len(self.disagg_prefill_inflight_queue) == 0:
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
             # HACK (byronhsu): reset the batch_is_full flag because we never enter update_running_batch which resets it

python/sglang/srt/managers/scheduler.py

@@ -179,6 +179,27 @@ class EmbeddingBatchResult:
     bid: int
 
 
+class IdleSleeper:
+    """
+    In setups which have long inactivity periods it is desirable to reduce
+    system power consumption when sglang does nothing. This would lead not only
+    to power savings, but also to more CPU thermal headroom when a request
+    eventually comes. This is important in cases when multiple GPUs are connected
+    as each GPU would otherwise pin one thread at 100% CPU usage.
+
+    The simplest solution is to use zmq.Poller on all sockets that may receive
+    data that needs handling immediately.
+    """
+
+    def __init__(self, sockets):
+        self.poller = zmq.Poller()
+        for s in sockets:
+            self.poller.register(s, zmq.POLLIN)
+
+    def maybe_sleep(self):
+        self.poller.poll(1000)
+
+
 class Scheduler(
     SchedulerOutputProcessorMixin,
     SchedulerDisaggregationDecodeMixin,
@@ -228,6 +249,8 @@ class Scheduler(
 
         # Init inter-process communication
         context = zmq.Context(2)
+        self.idle_sleeper = None
+
         if self.pp_rank == 0 and self.attn_tp_rank == 0:
             self.recv_from_tokenizer = get_zmq_socket(
                 context, zmq.PULL, port_args.scheduler_input_ipc_name, False
@@ -250,6 +273,13 @@ class Scheduler(
             self.recv_from_rpc = get_zmq_socket(
                 context, zmq.DEALER, port_args.rpc_ipc_name, False
             )
+            if self.server_args.sleep_on_idle:
+                self.idle_sleeper = IdleSleeper(
+                    [
+                        self.recv_from_tokenizer,
+                        self.recv_from_rpc,
+                    ]
+                )
         else:
             self.recv_from_tokenizer = None
             self.recv_from_rpc = None
@@ -478,6 +508,10 @@ class Scheduler(
         )
         self.init_disaggregation()
 
+    def maybe_sleep_on_idle(self):
+        if self.idle_sleeper is not None:
+            self.idle_sleeper.maybe_sleep()
+
     def init_tokenizer(self):
         server_args = self.server_args
 
@@ -667,6 +701,7 @@ class Scheduler(
                 # When the server is idle, do self-check and re-init some states
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
 
@@ -711,6 +746,7 @@ class Scheduler(
                 # When the server is idle, do self-check and re-init some states
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
             self.last_batch = batch
 
@@ -816,6 +852,7 @@ class Scheduler(
             if server_is_idle:
                 self.check_memory()
                 self.new_token_ratio = self.init_new_token_ratio
+                self.maybe_sleep_on_idle()
 
     def recv_requests(self) -> List[Req]:
         """Receive results at tp_rank = 0 and broadcast it to all other TP ranks."""

python/sglang/srt/server_args.py

@@ -90,6 +90,7 @@ class ServerArgs:
     download_dir: Optional[str] = None
     base_gpu_id: int = 0
     gpu_id_step: int = 1
+    sleep_on_idle: bool = False
 
     # Logging
     log_level: str = "info"
@@ -844,6 +845,11 @@ class ServerArgs:
             default=ServerArgs.gpu_id_step,
             help="The delta between consecutive GPU IDs that are used. For example, setting it to 2 will use GPU 0,2,4,...",
         )
+        parser.add_argument(
+            "--sleep-on-idle",
+            action="store_true",
+            help="Reduce CPU usage when sglang is idle.",
+        )
 
         # Logging
         parser.add_argument(