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Subject[tip:x86/spinlocks] x86, ticketlock: Clean up types and accessors
Commit-ID:  699f3dd4e4f8fba6ded83a3dc21e3db960323fcc
Gitweb: http://git.kernel.org/tip/699f3dd4e4f8fba6ded83a3dc21e3db960323fcc
Author: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
AuthorDate: Thu, 23 Jun 2011 18:19:13 -0700
Committer: H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Fri, 22 Jul 2011 11:13:17 -0700

x86, ticketlock: Clean up types and accessors

A few cleanups to the way spinlocks are defined and accessed:
- define __ticket_t which is the size of a spinlock ticket (ie, enough
bits to hold all the cpus)
- Define struct arch_spinlock as a union containing plain slock and
the head and tail tickets
- Use head and tail to implement some of the spinlock predicates.
- Make all ticket variables unsigned.
- Use TICKET_SHIFT to form constants

Most of this will be used in later patches.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Link: http://lkml.kernel.org/r/05552e1c97739f589cb76c20b5a6565ccd506636.1308878118.git.jeremy.fitzhardinge@citrix.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
arch/x86/include/asm/spinlock.h | 24 ++++++++++--------------
arch/x86/include/asm/spinlock_types.h | 20 ++++++++++++++++++--
2 files changed, 28 insertions(+), 16 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 3089f70..d6d5784 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -56,11 +56,9 @@
* much between them in performance though, especially as locks are out of line.
*/
#if (NR_CPUS < 256)
-#define TICKET_SHIFT 8
-
static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
{
- short inc = 0x0100;
+ unsigned short inc = 1 << TICKET_SHIFT;

asm volatile (
LOCK_PREFIX "xaddw %w0, %1\n"
@@ -79,7 +77,7 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)

static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
{
- int tmp, new;
+ unsigned int tmp, new;

asm volatile("movzwl %2, %0\n\t"
"cmpb %h0,%b0\n\t"
@@ -104,12 +102,10 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
: "memory", "cc");
}
#else
-#define TICKET_SHIFT 16
-
static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
{
- int inc = 0x00010000;
- int tmp;
+ unsigned inc = 1 << TICKET_SHIFT;
+ unsigned tmp;

asm volatile(LOCK_PREFIX "xaddl %0, %1\n"
"movzwl %w0, %2\n\t"
@@ -129,8 +125,8 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)

static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
{
- int tmp;
- int new;
+ unsigned tmp;
+ unsigned new;

asm volatile("movl %2,%0\n\t"
"movl %0,%1\n\t"
@@ -160,16 +156,16 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)

static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
{
- int tmp = ACCESS_ONCE(lock->slock);
+ struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

- return !!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1 << TICKET_SHIFT) - 1));
+ return !!(tmp.tail ^ tmp.head);
}

static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
{
- int tmp = ACCESS_ONCE(lock->slock);
+ struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

- return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
+ return ((tmp.tail - tmp.head) & TICKET_MASK) > 1;
}

#ifndef CONFIG_PARAVIRT_SPINLOCKS
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index dcb48b2..e3ad1e3 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -5,11 +5,27 @@
# error "please don't include this file directly"
#endif

+#include <linux/types.h>
+
+#if (CONFIG_NR_CPUS < 256)
+typedef u8 __ticket_t;
+#else
+typedef u16 __ticket_t;
+#endif
+
+#define TICKET_SHIFT (sizeof(__ticket_t) * 8)
+#define TICKET_MASK ((__ticket_t)((1 << TICKET_SHIFT) - 1))
+
typedef struct arch_spinlock {
- unsigned int slock;
+ union {
+ unsigned int slock;
+ struct __raw_tickets {
+ __ticket_t head, tail;
+ } tickets;
+ };
} arch_spinlock_t;

-#define __ARCH_SPIN_LOCK_UNLOCKED { 0 }
+#define __ARCH_SPIN_LOCK_UNLOCKED { { .slock = 0 } }

typedef struct {
unsigned int lock;

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