linux-kernel - [patch] spinlock_debug: don't recompute (jiffies_per

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Date:	Fri, 21 Jul 2006 18:30:57 -0400
From:	Chuck Ebbert <76306.1226@...puserve.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>
Subject: [patch] spinlock_debug: don't recompute (jiffies_per_loop *
  HZ) in spinloop

In spinlock_debug.c, the spinloops call __delay() on every iteration.
Because that is an external function, (jiffies_per_loop * HZ), the
loop's iteration limit, gets recomputed every time. Caching it
explicitly prevents that.

Signed-off-by: Chuck Ebbert <76306.1226@...puserve.com>

---

__delay() should really be declared __attribute_pure.


--- 2.6.18-rc2-64-numa.orig/lib/spinlock_debug.c
+++ 2.6.18-rc2-64-numa/lib/spinlock_debug.c
@@ -99,11 +99,12 @@ static inline void debug_spin_unlock(spi
 
 static void __spin_lock_debug(spinlock_t *lock)
 {
-	int print_once = 1;
 	u64 i;
+	u64 loops = loops_per_jiffy * HZ;
+	int print_once = 1;
 
 	for (;;) {
-		for (i = 0; i < loops_per_jiffy * HZ; i++) {
+		for (i = 0; i < loops; i++) {
 			if (__raw_spin_trylock(&lock->raw_lock))
 				return;
 			__delay(1);
@@ -164,11 +165,12 @@ static void rwlock_bug(rwlock_t *lock, c
 
 static void __read_lock_debug(rwlock_t *lock)
 {
-	int print_once = 1;
 	u64 i;
+	u64 loops = loops_per_jiffy * HZ;
+	int print_once = 1;
 
 	for (;;) {
-		for (i = 0; i < loops_per_jiffy * HZ; i++) {
+		for (i = 0; i < loops; i++) {
 			if (__raw_read_trylock(&lock->raw_lock))
 				return;
 			__delay(1);
@@ -237,11 +239,12 @@ static inline void debug_write_unlock(rw
 
 static void __write_lock_debug(rwlock_t *lock)
 {
-	int print_once = 1;
 	u64 i;
+	u64 loops = loops_per_jiffy * HZ;
+	int print_once = 1;
 
 	for (;;) {
-		for (i = 0; i < loops_per_jiffy * HZ; i++) {
+		for (i = 0; i < loops; i++) {
 			if (__raw_write_trylock(&lock->raw_lock))
 				return;
 			__delay(1);
-- 
Chuck
-
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