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Subject[PATCH v16 07/14] qspinlock: Revert to test-and-set on hypervisors
Date
From: Peter Zijlstra (Intel) <peterz@infradead.org>

When we detect a hypervisor (!paravirt, see qspinlock paravirt support
patches), revert to a simple test-and-set lock to avoid the horrors
of queue preemption.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
arch/x86/include/asm/qspinlock.h | 14 ++++++++++++++
include/asm-generic/qspinlock.h | 7 +++++++
kernel/locking/qspinlock.c | 3 +++
3 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 222995b..64c925e 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -1,6 +1,7 @@
#ifndef _ASM_X86_QSPINLOCK_H
#define _ASM_X86_QSPINLOCK_H

+#include <asm/cpufeature.h>
#include <asm-generic/qspinlock_types.h>

#define queue_spin_unlock queue_spin_unlock
@@ -15,6 +16,19 @@ static inline void queue_spin_unlock(struct qspinlock *lock)
smp_store_release((u8 *)lock, 0);
}

+#define virt_queue_spin_lock virt_queue_spin_lock
+
+static inline bool virt_queue_spin_lock(struct qspinlock *lock)
+{
+ if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+ return false;
+
+ while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)
+ cpu_relax();
+
+ return true;
+}
+
#include <asm-generic/qspinlock.h>

#endif /* _ASM_X86_QSPINLOCK_H */
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 315d6dc..bcbbc5e 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -111,6 +111,13 @@ static inline void queue_spin_unlock_wait(struct qspinlock *lock)
cpu_relax();
}

+#ifndef virt_queue_spin_lock
+static __always_inline bool virt_queue_spin_lock(struct qspinlock *lock)
+{
+ return false;
+}
+#endif
+
/*
* Initializier
*/
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 99503ef..fc2e5ab 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -249,6 +249,9 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val)

BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));

+ if (virt_queue_spin_lock(lock))
+ return;
+
/*
* wait for in-progress pending->locked hand-overs
*
--
1.7.1


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