From ff383d96babf5c44493c34606ef7485e25d08507 Mon Sep 17 00:00:00 2001
From: Balazs Gerofi <bgerofi@riken.jp>
Date: Wed, 7 Feb 2018 19:27:33 +0900
Subject: [PATCH] spinlock: rewrite spinlock to use Linux ticket head/tail
 format

This is a cherry-pick of 2964302d094f035242d6257d8af5450f72f9b5a7.

Change-Id: Ie8b7e825b28415dd41cc232fbeceb4653251f9e3
---
 arch/x86_64/kernel/include/arch-lock.h | 67 ++++++++++++--------------
 1 file changed, 32 insertions(+), 35 deletions(-)

diff --git a/arch/x86_64/kernel/include/arch-lock.h b/arch/x86_64/kernel/include/arch-lock.h
index f66b66df..5e318ded 100644
--- a/arch/x86_64/kernel/include/arch-lock.h
+++ b/arch/x86_64/kernel/include/arch-lock.h
@@ -14,7 +14,17 @@
 int __kprintf(const char *format, ...);
 #endif
 
-typedef int ihk_spinlock_t;
+typedef unsigned short __ticket_t;
+typedef unsigned int __ticketpair_t;
+
+typedef struct ihk_spinlock {
+	union {
+		__ticketpair_t head_tail;
+		struct __raw_tickets {
+			__ticket_t head, tail;
+		} tickets;
+	};
+} ihk_spinlock_t;
 
 extern void preempt_enable(void);
 extern void preempt_disable(void);
@@ -23,9 +33,9 @@ extern void preempt_disable(void);
 
 static void ihk_mc_spinlock_init(ihk_spinlock_t *lock)
 {
-	*lock = 0;
+	lock->head_tail = 0;
 }
-#define SPIN_LOCK_UNLOCKED 0
+#define SPIN_LOCK_UNLOCKED { .head_tail = 0 }
 
 #ifdef DEBUG_SPINLOCK
 #define ihk_mc_spinlock_lock_noirq(l) { \
@@ -39,40 +49,24 @@ __kprintf("[%d] ret ihk_mc_spinlock_lock_noirq\n", ihk_mc_get_processor_id()); \
 
 static void __ihk_mc_spinlock_lock_noirq(ihk_spinlock_t *lock)
 {
-	int inc = 0x00010000;
-	int tmp;
-
-#if 0
-	asm volatile("lock ; xaddl %0, %1\n"
-	             "movzwl %w0, %2\n\t"
-	             "shrl $16, %0\n\t"
-	             "1:\t"
-	             "cmpl %0, %2\n\t"
-	             "je 2f\n\t"
-	             "rep ; nop\n\t"
-	             "movzwl %1, %2\n\t"
-	             "jmp 1b\n"
-	             "2:"
-	             : "+Q" (inc), "+m" (*lock), "=r" (tmp) : : "memory", "cc");
-#endif
+	register struct __raw_tickets inc = { .tail = 0x0002 };
 
 	preempt_disable();
 
-	asm volatile("lock; xaddl %0, %1\n"
-			"movzwl %w0, %2\n\t"
-			"shrl $16, %0\n\t"
-			"1:\t"
-			"cmpl %0, %2\n\t"
-			"je 2f\n\t"
-			"rep ; nop\n\t"
-			"movzwl %1, %2\n\t"
-			/* don't need lfence here, because loads are in-order */
-			"jmp 1b\n"
-			"2:"
-			: "+r" (inc), "+m" (*lock), "=&r" (tmp)
-			:
-			: "memory", "cc");
+	asm volatile ("lock xaddl %0, %1\n"
+			: "+r" (inc), "+m" (*(lock)) : : "memory", "cc");
 
+	if (inc.head == inc.tail)
+		goto out;
+
+	for (;;) {
+		if (*((volatile __ticket_t *)&lock->tickets.head) == inc.tail)
+			goto out;
+		cpu_pause();
+	}
+
+out:
+	barrier();	/* make sure nothing creeps before the lock is taken */
 }
 
 #ifdef DEBUG_SPINLOCK
@@ -106,8 +100,11 @@ __kprintf("[%d] ret ihk_mc_spinlock_unlock_noirq\n", ihk_mc_get_processor_id());
 #endif
 static void __ihk_mc_spinlock_unlock_noirq(ihk_spinlock_t *lock)
 {
-	asm volatile ("lock incw %0" : "+m"(*lock) : : "memory", "cc");
-	
+	__ticket_t inc = 0x0002;
+
+	asm volatile ("lock addw %1, %0\n"
+			: "+m" (lock->tickets.head) : "ri" (inc) : "memory", "cc");
+
 	preempt_enable();
 }