Skip unnecessary poll() syscall when no I/O watchers are active

Author: axcherednikov

.gitignore

@@ -38,6 +38,7 @@ run-tests.php
 *.swp
 *.swo
 *~
+php_test_results_*.txt
 .idea/
 .vscode/
 

README.md

@@ -196,11 +196,11 @@ Revolt v1.0.8 tested with all four available drivers ([StreamSelect, Ev, Event,
 
 | Benchmark | Revolt StreamSelect | Revolt Ev | Revolt Event | Revolt UV | ext-eventloop |
 |---|--:|--:|--:|--:|--:|
-| `defer()` | 755,979 ops/sec | 726,468 ops/sec | 741,084 ops/sec | 730,488 ops/sec | **3,696,132 ops/sec** |
-| `delay(0)` | 245,389 ops/sec | 480,866 ops/sec | 467,362 ops/sec | 185,068 ops/sec | **3,041,443 ops/sec** |
-| `repeat(0)` | 694,763 ops/sec | 712,077 ops/sec | 74,929 ops/sec | 73,899 ops/sec | **17,971,855 ops/sec** |
-| I/O register + cancel | 2,149,497 ops/sec | 2,056,740 ops/sec | 2,034,001 ops/sec | 2,000,214 ops/sec | **7,642,510 ops/sec** |
-| Fiber suspend/resume | 219,349 ops/sec | 217,095 ops/sec | 220,924 ops/sec | 215,305 ops/sec | **242,691 ops/sec** |
+| `defer()` | 765,598 ops/sec | 743,057 ops/sec | 733,417 ops/sec | 742,926 ops/sec | **3,658,412 ops/sec** |
+| `delay(0)` | 242,383 ops/sec | 486,501 ops/sec | 464,196 ops/sec | 183,585 ops/sec | **3,047,625 ops/sec** |
+| `repeat(0)` | 687,196 ops/sec | 707,010 ops/sec | 74,708 ops/sec | 73,491 ops/sec | **17,371,529 ops/sec** |
+| I/O register + cancel | 2,114,361 ops/sec | 2,003,474 ops/sec | 1,980,326 ops/sec | 1,953,935 ops/sec | **7,193,404 ops/sec** |
+| Fiber suspend/resume | 221,383 ops/sec | 220,659 ops/sec | 218,318 ops/sec | 220,244 ops/sec | **243,242 ops/sec** |
 
 > These benchmarks measure callback dispatch and scheduling throughput. The I/O backend (StreamSelect, Ev, Event, UV) primarily affects polling efficiency at high concurrency, not dispatch speed — that's why all four Revolt drivers show similar numbers here. ext-eventloop moves the entire dispatch path into C, which is where the difference comes from. Fiber performance is nearly identical because `suspend()`/`resume()` is handled by the Zend Engine directly.
 >

eventloop.c

@@ -571,6 +571,7 @@ ZEND_METHOD(EventLoop_EventLoop, onReadable)
 		}
 	}
 
+	EVENTLOOP_G(io_watcher_count)++;
 	RETURN_STR_COPY(cb->id);
 }
 /* }}} */
@@ -605,6 +606,7 @@ ZEND_METHOD(EventLoop_EventLoop, onWritable)
 		}
 	}
 
+	EVENTLOOP_G(io_watcher_count)++;
 	RETURN_STR_COPY(cb->id);
 }
 /* }}} */
@@ -917,9 +919,13 @@ ZEND_METHOD(EventLoop_EventLoop, run)
 			}
 		}
 
-		EVENTLOOP_G(driver)->poll(timeout);
-		if (EVENTLOOP_G(stopped)) {
-			break;
+		/* Skip the syscall when there are no I/O watchers — avoids
+		 * unnecessary kevent()/epoll_wait()/poll() overhead on every tick */
+		if (EVENTLOOP_G(io_watcher_count) > 0 || timeout > 0) {
+			EVENTLOOP_G(driver)->poll(timeout);
+			if (EVENTLOOP_G(stopped)) {
+				break;
+			}
 		}
 
 		eventloop_process_timers();
@@ -1086,6 +1092,7 @@ PHP_RINIT_FUNCTION(eventloop)
 
 	EVENTLOOP_G(driver) = NULL;
 	EVENTLOOP_G(next_id) = 1;
+	EVENTLOOP_G(io_watcher_count) = 0;
 	EVENTLOOP_G(running) = false;
 	EVENTLOOP_G(stopped) = false;
 	ZVAL_NULL(&EVENTLOOP_G(error_handler));

eventloop_cb.c

@@ -118,6 +118,10 @@ void eventloop_cb_cancel(eventloop_callback *cb)
 		return;
 	}
 
+	if (cb->type == EVENTLOOP_CB_READABLE || cb->type == EVENTLOOP_CB_WRITABLE) {
+		EVENTLOOP_G(io_watcher_count)--;
+	}
+
 	eventloop_cb_disable(cb);
 	cb->flags |= EVENTLOOP_CB_FLAG_CANCELLED;
 	cb->flags &= ~EVENTLOOP_CB_FLAG_ENABLED;

php_eventloop.h

@@ -118,6 +118,7 @@ ZEND_BEGIN_MODULE_GLOBALS(eventloop)
 	eventloop_driver *driver;
 
 	uint64_t next_id;
+	uint32_t io_watcher_count;
 	bool running;
 	bool stopped;