ioq: Don't unroll the spin loop

tavianator · Jan 16, 2025 · 95bc3ed · 95bc3ed
1 parent f045573
commit 95bc3ed
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Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/src/bfs.h b/src/bfs.h
@@ -218,4 +218,15 @@ extern const char bfs_ldlibs[];
 #  define _target_clones(...)
 #endif
 
+/**
+ * Optimization hint to not unroll a loop.
+ */
+#if __clang__
+#  define _nounroll _Pragma("nounroll")
+#elif __GNUC__
+#  define _nounroll _Pragma("GCC unroll 0")
+#else
+#  define _nounroll
+#endif
+
 #endif // BFS_H
diff --git a/src/ioq.c b/src/ioq.c
@@ -277,10 +277,13 @@ static struct ioq_monitor *ioq_slot_monitor(struct ioqq *ioqq, ioq_slot *slot) {
 /** Atomically wait for a slot to change. */
 _noinline
 static uintptr_t ioq_slot_wait(struct ioqq *ioqq, ioq_slot *slot, uintptr_t value) {
-	// Try spinning a few times before blocking
 	uintptr_t ret;
+
+	// Try spinning a few times before blocking
+	_nounroll
 	for (int i = 0; i < 10; ++i) {
 		// Exponential backoff
+		_nounroll
 		for (int j = 0; j < (1 << i); ++j) {
 			spin_loop();
 		}