From 9c795fbdbf445d144d331ff2a19a0f42fe0fc190 Mon Sep 17 00:00:00 2001
From: Hector Martin <marcan@marcan.st>
Date: Mon, 30 May 2022 19:22:08 +0900
Subject: [PATCH] utils: Use WFE/SEV in spinlock

This should reduce memory traffic spam and power usage from lock
contention when threads are blocked on a spinlock.

Signed-off-by: Hector Martin <marcan@marcan.st>
---
 src/utils.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/utils.c b/src/utils.c
index 3c7133ac..314ba0d8 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -133,8 +133,10 @@ void spin_lock(spinlock_t *lock)
     s64 free = -1;
 
     while (!__atomic_compare_exchange_n(&lock->lock, &free, me, false, __ATOMIC_ACQUIRE,
-                                        __ATOMIC_RELAXED))
+                                        __ATOMIC_RELAXED)) {
         free = -1;
+        sysop("wfe");
+    }
 
     assert(__atomic_load_n(&lock->lock, __ATOMIC_RELAXED) == me);
     lock->count++;
@@ -147,6 +149,7 @@ void spin_unlock(spinlock_t *lock)
     assert(lock->count > 0);
     if (!--lock->count)
         __atomic_store_n(&lock->lock, -1L, __ATOMIC_RELEASE);
+    sysop("sev");
 }
 
 bool is_heap(void *addr)