[PATCH RFC 2/2] qspinlock x86: Enable x86 to use queue spinlock

[Waiman Long <Waiman.Long@hp.com>]

This patch makes the necessary changes at the x86 architecture specific
layer to enable the presence of the CONFIG_QUEUE_SPINLOCK kernel option
which can be used to replace the ticket spinlock by the queue spinlock.

The turning on of ARCH_QUEUE_SPINLOCK config option does not mean
that the ticket spinlock will be replaced. It only means that the
architecture supports the replacement. Actual replacement will only
happen if the QUEUE_SPINLOCK config option is also set.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
 arch/x86/Kconfig                      |    3 +++
 arch/x86/include/asm/spinlock.h       |    2 ++
 arch/x86/include/asm/spinlock_types.h |    4 ++++
 arch/x86/kernel/paravirt-spinlocks.c  |   10 ++++++++++
 4 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b32ebf9..8531e47 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2344,6 +2344,9 @@ config X86_DMA_REMAP
 	bool
 	depends on STA2X11
 
+config ARCH_QUEUE_SPINLOCK
+	def_bool y
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 33692ea..0ea805d 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -34,6 +34,7 @@
 # define UNLOCK_LOCK_PREFIX
 #endif
 
+#ifndef CONFIG_QUEUE_SPINLOCK
 /*
  * Ticket locks are conceptually two parts, one indicating the current head of
  * the queue, and the other indicating the current tail. The lock is acquired
@@ -130,6 +131,7 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
 }
 
 #endif	/* CONFIG_PARAVIRT_SPINLOCKS */
+#endif	/* !CONFIG_QUEUE_SPINLOCK */
 
 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 {
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index ad0ad07..8a7721e 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -7,6 +7,9 @@
 
 #include <linux/types.h>
 
+#ifdef CONFIG_QUEUE_SPINLOCK
+# include <asm-generic/qspinlock.h>
+#else
 #if (CONFIG_NR_CPUS < 256)
 typedef u8  __ticket_t;
 typedef u16 __ticketpair_t;
@@ -27,6 +30,7 @@ typedef struct arch_spinlock {
 } arch_spinlock_t;
 
 #define __ARCH_SPIN_LOCK_UNLOCKED	{ { 0 } }
+#endif
 
 #include <asm/rwlock.h>
 
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 676b8c7..75569cb 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -15,6 +15,15 @@ default_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
 
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
+# ifdef CONFIG_QUEUE_SPINLOCK
+	.spin_is_locked = queue_spin_is_locked,
+	.spin_is_contended = queue_spin_is_contended,
+
+	.spin_lock = queue_spin_lock,
+	.spin_lock_flags = default_spin_lock_flags,
+	.spin_trylock = queue_spin_trylock,
+	.spin_unlock = queue_spin_unlock,
+# else
 	.spin_is_locked = __ticket_spin_is_locked,
 	.spin_is_contended = __ticket_spin_is_contended,
 
@@ -22,6 +31,7 @@ struct pv_lock_ops pv_lock_ops = {
 	.spin_lock_flags = default_spin_lock_flags,
 	.spin_trylock = __ticket_spin_trylock,
 	.spin_unlock = __ticket_spin_unlock,
+# endif
 #endif
 };
 EXPORT_SYMBOL(pv_lock_ops);
-- 
1.7.1