[Xen-devel] [PATCH v14 02/11] qspinlock, x86: Enable x86-64 to use queue spinlock

[Waiman Long <Waiman.Long@xxxxxx>]

This patch makes the necessary changes at the x86 architecture
specific layer to enable the use of queue spinlock for x86-64. As
x86-32 machines are typically not multi-socket. The benefit of queue
spinlock may not be apparent. So queue spinlock is not enabled.

Currently, there is some incompatibilities between the para-virtualized
spinlock code (which hard-codes the use of ticket spinlock) and the
queue spinlock. Therefore, the use of queue spinlock is disabled when
the para-virtualized spinlock is enabled.

The arch/x86/include/asm/qspinlock.h header file includes some x86
specific optimization which will make the queue spinlock code perform
better than the generic implementation.

Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 arch/x86/Kconfig                      |    1 +
 arch/x86/include/asm/qspinlock.h      |   25 +++++++++++++++++++++++++
 arch/x86/include/asm/spinlock.h       |    5 +++++
 arch/x86/include/asm/spinlock_types.h |    4 ++++
 4 files changed, 35 insertions(+), 0 deletions(-)
 create mode 100644 arch/x86/include/asm/qspinlock.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ba397bd..420f057 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -123,6 +123,7 @@ config X86
        select MODULES_USE_ELF_RELA if X86_64
        select CLONE_BACKWARDS if X86_32
        select ARCH_USE_BUILTIN_BSWAP
+       select ARCH_USE_QUEUE_SPINLOCK
        select ARCH_USE_QUEUE_RWLOCK
        select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION
        select OLD_SIGACTION if X86_32
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
new file mode 100644
index 0000000..a6a8762
--- /dev/null
+++ b/arch/x86/include/asm/qspinlock.h
@@ -0,0 +1,25 @@
+#ifndef _ASM_X86_QSPINLOCK_H
+#define _ASM_X86_QSPINLOCK_H
+
+#include <asm-generic/qspinlock_types.h>
+
+#ifndef CONFIG_X86_PPRO_FENCE
+
+#define        queue_spin_unlock queue_spin_unlock
+/**
+ * queue_spin_unlock - release a queue spinlock
+ * @lock : Pointer to queue spinlock structure
+ *
+ * An effective smp_store_release() on the least-significant byte.
+ */
+static inline void queue_spin_unlock(struct qspinlock *lock)
+{
+       barrier();
+       ACCESS_ONCE(*(u8 *)lock) = 0;
+}
+
+#endif /* !CONFIG_X86_PPRO_FENCE */
+
+#include <asm-generic/qspinlock.h>
+
+#endif /* _ASM_X86_QSPINLOCK_H */
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 625660f..5a5b90c 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -42,6 +42,10 @@
 extern struct static_key paravirt_ticketlocks_enabled;
 static __always_inline bool static_key_false(struct static_key *key);
 
+#ifdef CONFIG_QUEUE_SPINLOCK
+#include <asm/qspinlock.h>
+#else
+
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 
 static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
@@ -198,6 +202,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t 
*lock)
                cpu_relax();
        }
 }
+#endif /* CONFIG_QUEUE_SPINLOCK */
 
 /*
  * Read-write spinlocks, allowing multiple readers
diff --git a/arch/x86/include/asm/spinlock_types.h 
b/arch/x86/include/asm/spinlock_types.h
index 5f9d757..5d654a1 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -23,6 +23,9 @@ typedef u32 __ticketpair_t;
 
 #define TICKET_SHIFT   (sizeof(__ticket_t) * 8)
 
+#ifdef CONFIG_QUEUE_SPINLOCK
+#include <asm-generic/qspinlock_types.h>
+#else
 typedef struct arch_spinlock {
        union {
                __ticketpair_t head_tail;
@@ -33,6 +36,7 @@ typedef struct arch_spinlock {
 } arch_spinlock_t;
 
 #define __ARCH_SPIN_LOCK_UNLOCKED      { { 0 } }
+#endif /* CONFIG_QUEUE_SPINLOCK */
 
 #include <asm-generic/qrwlock_types.h>
 
-- 
1.7.1


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