From 95bc3ed03bf192e3e62278850101fb94d46ab660 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 16 Jan 2025 14:19:25 -0500
Subject: [PATCH] ioq: Don't unroll the spin loop

---
 src/bfs.h | 11 +++++++++++
 src/ioq.c |  5 ++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/bfs.h b/src/bfs.h
index af4cf9f0..6c930ad4 100644
--- 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
index 8050c9e9..dd5d31e4 100644
--- 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();
 		}