[PATCH v9 1/6] powerpc/qspinlock: powerpc support qspinlock
Pan Xinhui
xinhui.pan at linux.vnet.ibm.com
Wed Dec 7 05:09:22 AEDT 2016
This patch add basic code to enable qspinlock on powerpc. qspinlock is
one kind of fairlock implementation. And seen some performance improvement
under some scenarios.
queued_spin_unlock() release the lock by just one write of NULL to the
::locked field which sits at different places in the two endianness
system.
We override some arch_spin_XXX as powerpc has io_sync stuff which makes
sure the io operations are protected by the lock correctly.
There is another special case, see commit
2c610022711 ("locking/qspinlock: Fix spin_unlock_wait() some more")
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
arch/powerpc/include/asm/qspinlock.h | 66 +++++++++++++++++++++++++++++++
arch/powerpc/include/asm/spinlock.h | 31 +++++++++------
arch/powerpc/include/asm/spinlock_types.h | 4 ++
arch/powerpc/lib/locks.c | 62 +++++++++++++++++++++++++++++
4 files changed, 150 insertions(+), 13 deletions(-)
create mode 100644 arch/powerpc/include/asm/qspinlock.h
diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
new file mode 100644
index 0000000..4c89256
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -0,0 +1,66 @@
+#ifndef _ASM_POWERPC_QSPINLOCK_H
+#define _ASM_POWERPC_QSPINLOCK_H
+
+#include <asm-generic/qspinlock_types.h>
+
+#define SPIN_THRESHOLD (1 << 15)
+#define queued_spin_unlock queued_spin_unlock
+#define queued_spin_is_locked queued_spin_is_locked
+#define queued_spin_unlock_wait queued_spin_unlock_wait
+
+extern void queued_spin_unlock_wait(struct qspinlock *lock);
+
+static inline u8 *__qspinlock_lock_byte(struct qspinlock *lock)
+{
+ return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
+}
+
+static inline void queued_spin_unlock(struct qspinlock *lock)
+{
+ /* release semantics is required */
+ smp_store_release(__qspinlock_lock_byte(lock), 0);
+}
+
+static inline int queued_spin_is_locked(struct qspinlock *lock)
+{
+ smp_mb();
+ return atomic_read(&lock->val);
+}
+
+#include <asm-generic/qspinlock.h>
+
+/* we need override it as ppc has io_sync stuff */
+#undef arch_spin_trylock
+#undef arch_spin_lock
+#undef arch_spin_lock_flags
+#undef arch_spin_unlock
+#define arch_spin_trylock arch_spin_trylock
+#define arch_spin_lock arch_spin_lock
+#define arch_spin_lock_flags arch_spin_lock_flags
+#define arch_spin_unlock arch_spin_unlock
+
+static inline int arch_spin_trylock(arch_spinlock_t *lock)
+{
+ CLEAR_IO_SYNC;
+ return queued_spin_trylock(lock);
+}
+
+static inline void arch_spin_lock(arch_spinlock_t *lock)
+{
+ CLEAR_IO_SYNC;
+ queued_spin_lock(lock);
+}
+
+static inline
+void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
+{
+ CLEAR_IO_SYNC;
+ queued_spin_lock(lock);
+}
+
+static inline void arch_spin_unlock(arch_spinlock_t *lock)
+{
+ SYNC_IO;
+ queued_spin_unlock(lock);
+}
+#endif /* _ASM_POWERPC_QSPINLOCK_H */
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 8c1b913..954099e 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -60,6 +60,23 @@ static inline bool vcpu_is_preempted(int cpu)
}
#endif
+#if defined(CONFIG_PPC_SPLPAR)
+/* We only yield to the hypervisor if we are in shared processor mode */
+#define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr))
+extern void __spin_yield(arch_spinlock_t *lock);
+extern void __rw_yield(arch_rwlock_t *lock);
+#else /* SPLPAR */
+#define __spin_yield(x) barrier()
+#define __rw_yield(x) barrier()
+#define SHARED_PROCESSOR 0
+#endif
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+#include <asm/qspinlock.h>
+#else
+
+#define arch_spin_relax(lock) __spin_yield(lock)
+
static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return lock.slock == 0;
@@ -114,18 +131,6 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
* held. Conveniently, we have a word in the paca that holds this
* value.
*/
-
-#if defined(CONFIG_PPC_SPLPAR)
-/* We only yield to the hypervisor if we are in shared processor mode */
-#define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr))
-extern void __spin_yield(arch_spinlock_t *lock);
-extern void __rw_yield(arch_rwlock_t *lock);
-#else /* SPLPAR */
-#define __spin_yield(x) barrier()
-#define __rw_yield(x) barrier()
-#define SHARED_PROCESSOR 0
-#endif
-
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
CLEAR_IO_SYNC;
@@ -203,6 +208,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
smp_mb();
}
+#endif /* !CONFIG_QUEUED_SPINLOCKS */
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
@@ -338,7 +344,6 @@ static inline void arch_write_unlock(arch_rwlock_t *rw)
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
-#define arch_spin_relax(lock) __spin_yield(lock)
#define arch_read_relax(lock) __rw_yield(lock)
#define arch_write_relax(lock) __rw_yield(lock)
diff --git a/arch/powerpc/include/asm/spinlock_types.h b/arch/powerpc/include/asm/spinlock_types.h
index 2351adc..bd7144e 100644
--- a/arch/powerpc/include/asm/spinlock_types.h
+++ b/arch/powerpc/include/asm/spinlock_types.h
@@ -5,11 +5,15 @@
# error "please don't include this file directly"
#endif
+#ifdef CONFIG_QUEUED_SPINLOCKS
+#include <asm-generic/qspinlock_types.h>
+#else
typedef struct {
volatile unsigned int slock;
} arch_spinlock_t;
#define __ARCH_SPIN_LOCK_UNLOCKED { 0 }
+#endif
typedef struct {
volatile signed int lock;
diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
index b7b1237..8f6dbb0 100644
--- a/arch/powerpc/lib/locks.c
+++ b/arch/powerpc/lib/locks.c
@@ -23,6 +23,7 @@
#include <asm/hvcall.h>
#include <asm/smp.h>
+#ifndef CONFIG_QUEUED_SPINLOCKS
void __spin_yield(arch_spinlock_t *lock)
{
unsigned int lock_value, holder_cpu, yield_count;
@@ -42,6 +43,7 @@ void __spin_yield(arch_spinlock_t *lock)
get_hard_smp_processor_id(holder_cpu), yield_count);
}
EXPORT_SYMBOL_GPL(__spin_yield);
+#endif
/*
* Waiting for a read lock or a write lock on a rwlock...
@@ -68,3 +70,63 @@ void __rw_yield(arch_rwlock_t *rw)
get_hard_smp_processor_id(holder_cpu), yield_count);
}
#endif
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+/*
+ * This forbid we load an old value in another LL/SC. Because the SC here force
+ * another LL/SC repeat. So we guarantee all loads in another LL and SC will
+ * read correct value.
+ */
+static inline u32 atomic_read_sync(atomic_t *v)
+{
+ u32 val;
+
+ __asm__ __volatile__(
+"1: " PPC_LWARX(%0, 0, %2, 0) "\n"
+" stwcx. %0, 0, %2\n"
+" bne- 1b\n"
+ : "=&r" (val), "+m" (*v)
+ : "r" (v)
+ : "cr0", "xer");
+
+ return val;
+}
+
+void queued_spin_unlock_wait(struct qspinlock *lock)
+{
+
+ u32 val;
+
+ smp_mb();
+
+ /*
+ * copied from generic queue_spin_unlock_wait with little modification
+ */
+ for (;;) {
+ /* need _sync, as we might race with another LL/SC in lock()*/
+ val = atomic_read_sync(&lock->val);
+
+ if (!val) /* not locked, we're done */
+ goto done;
+
+ if (val & _Q_LOCKED_MASK) /* locked, go wait for unlock */
+ break;
+
+ /* not locked, but pending, wait until we observe the lock */
+ cpu_relax();
+ }
+
+ /*
+ * any unlock is good.
+ * And _sync() is not needed here, because once we got here, we must
+ * already read the ->val as LOCKED via a _sync(). Combining the
+ * smp_mb() before, we guarantee that all the memory accesses before
+ * unlock_wait() must be observed by the next lock critical section.
+ */
+ while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
+ cpu_relax();
+done:
+ smp_mb();
+}
+EXPORT_SYMBOL(queued_spin_unlock_wait);
+#endif
--
2.4.11
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