From 2440a9d67b0785132e303ed6f12dff8e80baa547 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Wed, 14 Feb 2024 18:26:47 -0500
Subject: kernel: cpu: Add hint_spinwait()

This commit introduces a macro that must exist per
architecture (even if it does nothing) to ensure it is
machine independent.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/arch/amd64/cpu.h | 7 +++++++
 sys/kern/kern_sched.c        | 8 ++------
 2 files changed, 9 insertions(+), 6 deletions(-)

(limited to 'sys')

diff --git a/sys/include/arch/amd64/cpu.h b/sys/include/arch/amd64/cpu.h
index c72c106..e6f2de0 100644
--- a/sys/include/arch/amd64/cpu.h
+++ b/sys/include/arch/amd64/cpu.h
@@ -37,6 +37,13 @@
 #include <sys/queue.h>
 #include <machine/tss.h>
 #include <machine/msr.h>
+/*
+ * XXX: We are not using the PAUSE instruction for the sake of
+ *      ensuring compatibility... PAUSE is F3 90, REP NOP is
+ *      F3 90... REP NOP will be read as a PAUSE on processors
+ *      that support it.
+ */
+#define hint_spinwait() __ASMV("rep; nop")
 
 #define this_cpu()      amd64_this_cpu()
 #define get_bsp()       amd64_get_bsp()
diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
index da4c6c5..4f17ddf 100644
--- a/sys/kern/kern_sched.c
+++ b/sys/kern/kern_sched.c
@@ -32,6 +32,7 @@
 #include <sys/types.h>
 #include <sys/cdefs.h>
 #include <sys/spinlock.h>
+#include <machine/cpu.h>
 #include <assert.h>
 
 /*
@@ -59,17 +60,12 @@ sched_enqueue_ci(struct cpu_info *ci)
 
 /*
  * Processor awaiting tasks to be assigned will be here spinning.
- *
- * XXX: We are not using the PAUSE instruction for the sake of
- *      ensuring compatibility... PAUSE is F3 90, REP NOP is
- *      F3 90... REP NOP will be read as a PAUSE on processors
- *      that support it.
  */
 __noreturn static void
 sched_enter(void)
 {
     for (;;) {
-        __ASMV("rep; nop");
+        hint_spinwait();
     }
 }
 
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