mirror of
https://github.com/edk2-porting/linux-next.git
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Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar: "So we have a laundry list of locking subsystem changes: - continuing barrier API and code improvements - futex enhancements - atomics API improvements - pvqspinlock enhancements: in particular lock stealing and adaptive spinning - qspinlock micro-enhancements" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op futex: Cleanup the goto confusion in requeue_pi() futex: Remove pointless put_pi_state calls in requeue() futex: Document pi_state refcounting in requeue code futex: Rename free_pi_state() to put_pi_state() futex: Drop refcount if requeue_pi() acquired the rtmutex locking/barriers, arch: Remove ambiguous statement in the smp_store_mb() documentation lcoking/barriers, arch: Use smp barriers in smp_store_release() locking/cmpxchg, arch: Remove tas() definitions locking/pvqspinlock: Queue node adaptive spinning locking/pvqspinlock: Allow limited lock stealing locking/pvqspinlock: Collect slowpath lock statistics sched/core, locking: Document Program-Order guarantees locking, sched: Introduce smp_cond_acquire() and use it locking/pvqspinlock, x86: Optimize the PV unlock code path locking/qspinlock: Avoid redundant read of next pointer locking/qspinlock: Prefetch the next node cacheline locking/qspinlock: Use _acquire/_release() versions of cmpxchg() & xchg() atomics: Add test for atomic operations with _relaxed variants
This commit is contained in:
commit
24af98c4cf
@ -1673,8 +1673,8 @@ There are some more advanced barrier functions:
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(*) smp_store_mb(var, value)
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This assigns the value to the variable and then inserts a full memory
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barrier after it, depending on the function. It isn't guaranteed to
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insert anything more than a compiler barrier in a UP compilation.
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barrier after it. It isn't guaranteed to insert anything more than a
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compiler barrier in a UP compilation.
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(*) smp_mb__before_atomic();
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|
@ -128,6 +128,5 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
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#endif /* !CONFIG_SMP */
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#define xchg(ptr, x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr))))
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#define tas(ptr) ((void)xchg((ptr), 1))
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#endif /* __ARCH_BLACKFIN_CMPXCHG__ */
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|
@ -47,8 +47,6 @@ static inline unsigned int __xchg(unsigned int x, volatile void *ptr, int size)
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#define xchg(ptr, x) \
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((__typeof__(*(ptr)))__xchg((unsigned int)(x), (void *) (ptr), \
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sizeof(*(ptr))))
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#define tas(ptr) xchg((ptr), 1)
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#include <asm-generic/cmpxchg-local.h>
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@ -69,8 +69,6 @@ extern uint32_t __xchg_32(uint32_t i, volatile void *v);
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#endif
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#define tas(ptr) (xchg((ptr), 1))
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/*****************************************************************************/
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/*
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* compare and conditionally exchange value with memory
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@ -77,7 +77,7 @@ do { \
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___p1; \
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})
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0)
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
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/*
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* The group barrier in front of the rsm & ssm are necessary to ensure
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|
@ -34,7 +34,7 @@
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#define rmb() __asm__ __volatile__ ("sync" : : : "memory")
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#define wmb() __asm__ __volatile__ ("sync" : : : "memory")
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0)
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
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#ifdef __SUBARCH_HAS_LWSYNC
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# define SMPWMB LWSYNC
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|
@ -36,7 +36,7 @@
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#define smp_mb__before_atomic() smp_mb()
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#define smp_mb__after_atomic() smp_mb()
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0)
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
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#define smp_store_release(p, v) \
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do { \
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|
@ -127,8 +127,6 @@ long long _atomic64_cmpxchg(long long *v, long long o, long long n);
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#endif
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#define tas(ptr) xchg((ptr), 1)
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_TILE_CMPXCHG_H */
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|
@ -687,6 +687,14 @@ config PARAVIRT_SPINLOCKS
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If you are unsure how to answer this question, answer Y.
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config QUEUED_LOCK_STAT
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bool "Paravirt queued spinlock statistics"
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depends on PARAVIRT_SPINLOCKS && DEBUG_FS && QUEUED_SPINLOCKS
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---help---
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Enable the collection of statistical data on the slowpath
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behavior of paravirtualized queued spinlocks and report
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them on debugfs.
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source "arch/x86/xen/Kconfig"
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config KVM_GUEST
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|
@ -1,6 +1,65 @@
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#ifndef __ASM_QSPINLOCK_PARAVIRT_H
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#define __ASM_QSPINLOCK_PARAVIRT_H
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/*
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* For x86-64, PV_CALLEE_SAVE_REGS_THUNK() saves and restores 8 64-bit
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* registers. For i386, however, only 1 32-bit register needs to be saved
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* and restored. So an optimized version of __pv_queued_spin_unlock() is
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* hand-coded for 64-bit, but it isn't worthwhile to do it for 32-bit.
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*/
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#ifdef CONFIG_64BIT
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PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
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#define __pv_queued_spin_unlock __pv_queued_spin_unlock
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#define PV_UNLOCK "__raw_callee_save___pv_queued_spin_unlock"
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#define PV_UNLOCK_SLOWPATH "__raw_callee_save___pv_queued_spin_unlock_slowpath"
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/*
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* Optimized assembly version of __raw_callee_save___pv_queued_spin_unlock
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* which combines the registers saving trunk and the body of the following
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* C code:
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*
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* void __pv_queued_spin_unlock(struct qspinlock *lock)
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* {
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* struct __qspinlock *l = (void *)lock;
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* u8 lockval = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
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*
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* if (likely(lockval == _Q_LOCKED_VAL))
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* return;
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* pv_queued_spin_unlock_slowpath(lock, lockval);
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* }
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*
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* For x86-64,
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* rdi = lock (first argument)
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* rsi = lockval (second argument)
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* rdx = internal variable (set to 0)
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*/
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asm (".pushsection .text;"
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".globl " PV_UNLOCK ";"
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".align 4,0x90;"
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PV_UNLOCK ": "
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"push %rdx;"
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"mov $0x1,%eax;"
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"xor %edx,%edx;"
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"lock cmpxchg %dl,(%rdi);"
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"cmp $0x1,%al;"
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"jne .slowpath;"
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"pop %rdx;"
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"ret;"
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".slowpath: "
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"push %rsi;"
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"movzbl %al,%esi;"
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"call " PV_UNLOCK_SLOWPATH ";"
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"pop %rsi;"
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"pop %rdx;"
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"ret;"
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".size " PV_UNLOCK ", .-" PV_UNLOCK ";"
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".popsection");
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#else /* CONFIG_64BIT */
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extern void __pv_queued_spin_unlock(struct qspinlock *lock);
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PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock);
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#endif /* CONFIG_64BIT */
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#endif
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|
@ -93,7 +93,7 @@
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#endif /* CONFIG_SMP */
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0)
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
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#endif
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#ifndef smp_mb__before_atomic
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|
@ -12,8 +12,9 @@
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* GNU General Public License for more details.
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*
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* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
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* (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
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*
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* Authors: Waiman Long <waiman.long@hp.com>
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* Authors: Waiman Long <waiman.long@hpe.com>
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*/
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#ifndef __ASM_GENERIC_QSPINLOCK_H
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#define __ASM_GENERIC_QSPINLOCK_H
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@ -62,7 +63,7 @@ static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
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static __always_inline int queued_spin_trylock(struct qspinlock *lock)
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{
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if (!atomic_read(&lock->val) &&
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(atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0))
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(atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0))
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return 1;
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return 0;
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}
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@ -77,7 +78,7 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock)
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{
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u32 val;
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val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL);
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val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL);
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if (likely(val == 0))
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return;
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queued_spin_lock_slowpath(lock, val);
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@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
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/*
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* smp_mb__before_atomic() in order to guarantee release semantics
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*/
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smp_mb__before_atomic_dec();
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smp_mb__before_atomic();
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atomic_sub(_Q_LOCKED_VAL, &lock->val);
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}
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#endif
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|
@ -299,6 +299,23 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
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__u.__val; \
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})
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/**
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* smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
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* @cond: boolean expression to wait for
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*
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* Equivalent to using smp_load_acquire() on the condition variable but employs
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* the control dependency of the wait to reduce the barrier on many platforms.
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*
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* The control dependency provides a LOAD->STORE order, the additional RMB
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* provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
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* aka. ACQUIRE.
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*/
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#define smp_cond_acquire(cond) do { \
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while (!(cond)) \
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cpu_relax(); \
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smp_rmb(); /* ctrl + rmb := acquire */ \
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} while (0)
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#endif /* __KERNEL__ */
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#endif /* __ASSEMBLY__ */
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|
@ -725,9 +725,12 @@ static struct futex_pi_state * alloc_pi_state(void)
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}
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/*
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* Drops a reference to the pi_state object and frees or caches it
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* when the last reference is gone.
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*
|
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* Must be called with the hb lock held.
|
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*/
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static void free_pi_state(struct futex_pi_state *pi_state)
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static void put_pi_state(struct futex_pi_state *pi_state)
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{
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if (!pi_state)
|
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return;
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@ -1706,31 +1709,35 @@ retry_private:
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* exist yet, look it up one more time to ensure we have a
|
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* reference to it. If the lock was taken, ret contains the
|
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* vpid of the top waiter task.
|
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* If the lock was not taken, we have pi_state and an initial
|
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* refcount on it. In case of an error we have nothing.
|
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*/
|
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if (ret > 0) {
|
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WARN_ON(pi_state);
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drop_count++;
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task_count++;
|
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/*
|
||||
* If we acquired the lock, then the user
|
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* space value of uaddr2 should be vpid. It
|
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* cannot be changed by the top waiter as it
|
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* is blocked on hb2 lock if it tries to do
|
||||
* so. If something fiddled with it behind our
|
||||
* back the pi state lookup might unearth
|
||||
* it. So we rather use the known value than
|
||||
* rereading and handing potential crap to
|
||||
* lookup_pi_state.
|
||||
* If we acquired the lock, then the user space value
|
||||
* of uaddr2 should be vpid. It cannot be changed by
|
||||
* the top waiter as it is blocked on hb2 lock if it
|
||||
* tries to do so. If something fiddled with it behind
|
||||
* our back the pi state lookup might unearth it. So
|
||||
* we rather use the known value than rereading and
|
||||
* handing potential crap to lookup_pi_state.
|
||||
*
|
||||
* If that call succeeds then we have pi_state and an
|
||||
* initial refcount on it.
|
||||
*/
|
||||
ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
|
||||
}
|
||||
|
||||
switch (ret) {
|
||||
case 0:
|
||||
/* We hold a reference on the pi state. */
|
||||
break;
|
||||
|
||||
/* If the above failed, then pi_state is NULL */
|
||||
case -EFAULT:
|
||||
free_pi_state(pi_state);
|
||||
pi_state = NULL;
|
||||
double_unlock_hb(hb1, hb2);
|
||||
hb_waiters_dec(hb2);
|
||||
put_futex_key(&key2);
|
||||
@ -1746,8 +1753,6 @@ retry_private:
|
||||
* exit to complete.
|
||||
* - The user space value changed.
|
||||
*/
|
||||
free_pi_state(pi_state);
|
||||
pi_state = NULL;
|
||||
double_unlock_hb(hb1, hb2);
|
||||
hb_waiters_dec(hb2);
|
||||
put_futex_key(&key2);
|
||||
@ -1801,30 +1806,58 @@ retry_private:
|
||||
* of requeue_pi if we couldn't acquire the lock atomically.
|
||||
*/
|
||||
if (requeue_pi) {
|
||||
/* Prepare the waiter to take the rt_mutex. */
|
||||
/*
|
||||
* Prepare the waiter to take the rt_mutex. Take a
|
||||
* refcount on the pi_state and store the pointer in
|
||||
* the futex_q object of the waiter.
|
||||
*/
|
||||
atomic_inc(&pi_state->refcount);
|
||||
this->pi_state = pi_state;
|
||||
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
||||
this->rt_waiter,
|
||||
this->task);
|
||||
if (ret == 1) {
|
||||
/* We got the lock. */
|
||||
/*
|
||||
* We got the lock. We do neither drop the
|
||||
* refcount on pi_state nor clear
|
||||
* this->pi_state because the waiter needs the
|
||||
* pi_state for cleaning up the user space
|
||||
* value. It will drop the refcount after
|
||||
* doing so.
|
||||
*/
|
||||
requeue_pi_wake_futex(this, &key2, hb2);
|
||||
drop_count++;
|
||||
continue;
|
||||
} else if (ret) {
|
||||
/* -EDEADLK */
|
||||
/*
|
||||
* rt_mutex_start_proxy_lock() detected a
|
||||
* potential deadlock when we tried to queue
|
||||
* that waiter. Drop the pi_state reference
|
||||
* which we took above and remove the pointer
|
||||
* to the state from the waiters futex_q
|
||||
* object.
|
||||
*/
|
||||
this->pi_state = NULL;
|
||||
free_pi_state(pi_state);
|
||||
goto out_unlock;
|
||||
put_pi_state(pi_state);
|
||||
/*
|
||||
* We stop queueing more waiters and let user
|
||||
* space deal with the mess.
|
||||
*/
|
||||
break;
|
||||
}
|
||||
}
|
||||
requeue_futex(this, hb1, hb2, &key2);
|
||||
drop_count++;
|
||||
}
|
||||
|
||||
/*
|
||||
* We took an extra initial reference to the pi_state either
|
||||
* in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
|
||||
* need to drop it here again.
|
||||
*/
|
||||
put_pi_state(pi_state);
|
||||
|
||||
out_unlock:
|
||||
free_pi_state(pi_state);
|
||||
double_unlock_hb(hb1, hb2);
|
||||
wake_up_q(&wake_q);
|
||||
hb_waiters_dec(hb2);
|
||||
@ -1973,7 +2006,7 @@ static void unqueue_me_pi(struct futex_q *q)
|
||||
__unqueue_futex(q);
|
||||
|
||||
BUG_ON(!q->pi_state);
|
||||
free_pi_state(q->pi_state);
|
||||
put_pi_state(q->pi_state);
|
||||
q->pi_state = NULL;
|
||||
|
||||
spin_unlock(q->lock_ptr);
|
||||
@ -2755,6 +2788,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
||||
if (q.pi_state && (q.pi_state->owner != current)) {
|
||||
spin_lock(q.lock_ptr);
|
||||
ret = fixup_pi_state_owner(uaddr2, &q, current);
|
||||
/*
|
||||
* Drop the reference to the pi state which
|
||||
* the requeue_pi() code acquired for us.
|
||||
*/
|
||||
put_pi_state(q.pi_state);
|
||||
spin_unlock(q.lock_ptr);
|
||||
}
|
||||
} else {
|
||||
@ -3046,7 +3084,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
||||
|
||||
if (op & FUTEX_CLOCK_REALTIME) {
|
||||
flags |= FLAGS_CLOCKRT;
|
||||
if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
|
||||
if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
|
||||
cmd != FUTEX_WAIT_REQUEUE_PI)
|
||||
return -ENOSYS;
|
||||
}
|
||||
|
||||
|
@ -14,8 +14,9 @@
|
||||
* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
|
||||
* (C) Copyright 2013-2014 Red Hat, Inc.
|
||||
* (C) Copyright 2015 Intel Corp.
|
||||
* (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
|
||||
*
|
||||
* Authors: Waiman Long <waiman.long@hp.com>
|
||||
* Authors: Waiman Long <waiman.long@hpe.com>
|
||||
* Peter Zijlstra <peterz@infradead.org>
|
||||
*/
|
||||
|
||||
@ -176,7 +177,12 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
|
||||
return (u32)xchg(&l->tail, tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
|
||||
/*
|
||||
* Use release semantics to make sure that the MCS node is properly
|
||||
* initialized before changing the tail code.
|
||||
*/
|
||||
return (u32)xchg_release(&l->tail,
|
||||
tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
|
||||
}
|
||||
|
||||
#else /* _Q_PENDING_BITS == 8 */
|
||||
@ -208,7 +214,11 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
|
||||
|
||||
for (;;) {
|
||||
new = (val & _Q_LOCKED_PENDING_MASK) | tail;
|
||||
old = atomic_cmpxchg(&lock->val, val, new);
|
||||
/*
|
||||
* Use release semantics to make sure that the MCS node is
|
||||
* properly initialized before changing the tail code.
|
||||
*/
|
||||
old = atomic_cmpxchg_release(&lock->val, val, new);
|
||||
if (old == val)
|
||||
break;
|
||||
|
||||
@ -238,18 +248,20 @@ static __always_inline void set_locked(struct qspinlock *lock)
|
||||
*/
|
||||
|
||||
static __always_inline void __pv_init_node(struct mcs_spinlock *node) { }
|
||||
static __always_inline void __pv_wait_node(struct mcs_spinlock *node) { }
|
||||
static __always_inline void __pv_wait_node(struct mcs_spinlock *node,
|
||||
struct mcs_spinlock *prev) { }
|
||||
static __always_inline void __pv_kick_node(struct qspinlock *lock,
|
||||
struct mcs_spinlock *node) { }
|
||||
static __always_inline void __pv_wait_head(struct qspinlock *lock,
|
||||
struct mcs_spinlock *node) { }
|
||||
static __always_inline u32 __pv_wait_head_or_lock(struct qspinlock *lock,
|
||||
struct mcs_spinlock *node)
|
||||
{ return 0; }
|
||||
|
||||
#define pv_enabled() false
|
||||
|
||||
#define pv_init_node __pv_init_node
|
||||
#define pv_wait_node __pv_wait_node
|
||||
#define pv_kick_node __pv_kick_node
|
||||
#define pv_wait_head __pv_wait_head
|
||||
#define pv_wait_head_or_lock __pv_wait_head_or_lock
|
||||
|
||||
#ifdef CONFIG_PARAVIRT_SPINLOCKS
|
||||
#define queued_spin_lock_slowpath native_queued_spin_lock_slowpath
|
||||
@ -319,7 +331,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
|
||||
if (val == new)
|
||||
new |= _Q_PENDING_VAL;
|
||||
|
||||
old = atomic_cmpxchg(&lock->val, val, new);
|
||||
/*
|
||||
* Acquire semantic is required here as the function may
|
||||
* return immediately if the lock was free.
|
||||
*/
|
||||
old = atomic_cmpxchg_acquire(&lock->val, val, new);
|
||||
if (old == val)
|
||||
break;
|
||||
|
||||
@ -382,6 +398,7 @@ queue:
|
||||
* p,*,* -> n,*,*
|
||||
*/
|
||||
old = xchg_tail(lock, tail);
|
||||
next = NULL;
|
||||
|
||||
/*
|
||||
* if there was a previous node; link it and wait until reaching the
|
||||
@ -391,8 +408,18 @@ queue:
|
||||
prev = decode_tail(old);
|
||||
WRITE_ONCE(prev->next, node);
|
||||
|
||||
pv_wait_node(node);
|
||||
pv_wait_node(node, prev);
|
||||
arch_mcs_spin_lock_contended(&node->locked);
|
||||
|
||||
/*
|
||||
* While waiting for the MCS lock, the next pointer may have
|
||||
* been set by another lock waiter. We optimistically load
|
||||
* the next pointer & prefetch the cacheline for writing
|
||||
* to reduce latency in the upcoming MCS unlock operation.
|
||||
*/
|
||||
next = READ_ONCE(node->next);
|
||||
if (next)
|
||||
prefetchw(next);
|
||||
}
|
||||
|
||||
/*
|
||||
@ -406,11 +433,22 @@ queue:
|
||||
* sequentiality; this is because the set_locked() function below
|
||||
* does not imply a full barrier.
|
||||
*
|
||||
* The PV pv_wait_head_or_lock function, if active, will acquire
|
||||
* the lock and return a non-zero value. So we have to skip the
|
||||
* smp_load_acquire() call. As the next PV queue head hasn't been
|
||||
* designated yet, there is no way for the locked value to become
|
||||
* _Q_SLOW_VAL. So both the set_locked() and the
|
||||
* atomic_cmpxchg_relaxed() calls will be safe.
|
||||
*
|
||||
* If PV isn't active, 0 will be returned instead.
|
||||
*
|
||||
*/
|
||||
pv_wait_head(lock, node);
|
||||
while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK)
|
||||
cpu_relax();
|
||||
if ((val = pv_wait_head_or_lock(lock, node)))
|
||||
goto locked;
|
||||
|
||||
smp_cond_acquire(!((val = atomic_read(&lock->val)) & _Q_LOCKED_PENDING_MASK));
|
||||
|
||||
locked:
|
||||
/*
|
||||
* claim the lock:
|
||||
*
|
||||
@ -422,11 +460,17 @@ queue:
|
||||
* to grab the lock.
|
||||
*/
|
||||
for (;;) {
|
||||
if (val != tail) {
|
||||
/* In the PV case we might already have _Q_LOCKED_VAL set */
|
||||
if ((val & _Q_TAIL_MASK) != tail) {
|
||||
set_locked(lock);
|
||||
break;
|
||||
}
|
||||
old = atomic_cmpxchg(&lock->val, val, _Q_LOCKED_VAL);
|
||||
/*
|
||||
* The smp_load_acquire() call above has provided the necessary
|
||||
* acquire semantics required for locking. At most two
|
||||
* iterations of this loop may be ran.
|
||||
*/
|
||||
old = atomic_cmpxchg_relaxed(&lock->val, val, _Q_LOCKED_VAL);
|
||||
if (old == val)
|
||||
goto release; /* No contention */
|
||||
|
||||
@ -434,10 +478,12 @@ queue:
|
||||
}
|
||||
|
||||
/*
|
||||
* contended path; wait for next, release.
|
||||
* contended path; wait for next if not observed yet, release.
|
||||
*/
|
||||
while (!(next = READ_ONCE(node->next)))
|
||||
cpu_relax();
|
||||
if (!next) {
|
||||
while (!(next = READ_ONCE(node->next)))
|
||||
cpu_relax();
|
||||
}
|
||||
|
||||
arch_mcs_spin_unlock_contended(&next->locked);
|
||||
pv_kick_node(lock, next);
|
||||
@ -462,7 +508,7 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath);
|
||||
#undef pv_init_node
|
||||
#undef pv_wait_node
|
||||
#undef pv_kick_node
|
||||
#undef pv_wait_head
|
||||
#undef pv_wait_head_or_lock
|
||||
|
||||
#undef queued_spin_lock_slowpath
|
||||
#define queued_spin_lock_slowpath __pv_queued_spin_lock_slowpath
|
||||
|
@ -22,6 +22,20 @@
|
||||
|
||||
#define _Q_SLOW_VAL (3U << _Q_LOCKED_OFFSET)
|
||||
|
||||
/*
|
||||
* Queue Node Adaptive Spinning
|
||||
*
|
||||
* A queue node vCPU will stop spinning if the vCPU in the previous node is
|
||||
* not running. The one lock stealing attempt allowed at slowpath entry
|
||||
* mitigates the slight slowdown for non-overcommitted guest with this
|
||||
* aggressive wait-early mechanism.
|
||||
*
|
||||
* The status of the previous node will be checked at fixed interval
|
||||
* controlled by PV_PREV_CHECK_MASK. This is to ensure that we won't
|
||||
* pound on the cacheline of the previous node too heavily.
|
||||
*/
|
||||
#define PV_PREV_CHECK_MASK 0xff
|
||||
|
||||
/*
|
||||
* Queue node uses: vcpu_running & vcpu_halted.
|
||||
* Queue head uses: vcpu_running & vcpu_hashed.
|
||||
@ -40,6 +54,94 @@ struct pv_node {
|
||||
u8 state;
|
||||
};
|
||||
|
||||
/*
|
||||
* By replacing the regular queued_spin_trylock() with the function below,
|
||||
* it will be called once when a lock waiter enter the PV slowpath before
|
||||
* being queued. By allowing one lock stealing attempt here when the pending
|
||||
* bit is off, it helps to reduce the performance impact of lock waiter
|
||||
* preemption without the drawback of lock starvation.
|
||||
*/
|
||||
#define queued_spin_trylock(l) pv_queued_spin_steal_lock(l)
|
||||
static inline bool pv_queued_spin_steal_lock(struct qspinlock *lock)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
|
||||
return !(atomic_read(&lock->val) & _Q_LOCKED_PENDING_MASK) &&
|
||||
(cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0);
|
||||
}
|
||||
|
||||
/*
|
||||
* The pending bit is used by the queue head vCPU to indicate that it
|
||||
* is actively spinning on the lock and no lock stealing is allowed.
|
||||
*/
|
||||
#if _Q_PENDING_BITS == 8
|
||||
static __always_inline void set_pending(struct qspinlock *lock)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
|
||||
WRITE_ONCE(l->pending, 1);
|
||||
}
|
||||
|
||||
static __always_inline void clear_pending(struct qspinlock *lock)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
|
||||
WRITE_ONCE(l->pending, 0);
|
||||
}
|
||||
|
||||
/*
|
||||
* The pending bit check in pv_queued_spin_steal_lock() isn't a memory
|
||||
* barrier. Therefore, an atomic cmpxchg() is used to acquire the lock
|
||||
* just to be sure that it will get it.
|
||||
*/
|
||||
static __always_inline int trylock_clear_pending(struct qspinlock *lock)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
|
||||
return !READ_ONCE(l->locked) &&
|
||||
(cmpxchg(&l->locked_pending, _Q_PENDING_VAL, _Q_LOCKED_VAL)
|
||||
== _Q_PENDING_VAL);
|
||||
}
|
||||
#else /* _Q_PENDING_BITS == 8 */
|
||||
static __always_inline void set_pending(struct qspinlock *lock)
|
||||
{
|
||||
atomic_set_mask(_Q_PENDING_VAL, &lock->val);
|
||||
}
|
||||
|
||||
static __always_inline void clear_pending(struct qspinlock *lock)
|
||||
{
|
||||
atomic_clear_mask(_Q_PENDING_VAL, &lock->val);
|
||||
}
|
||||
|
||||
static __always_inline int trylock_clear_pending(struct qspinlock *lock)
|
||||
{
|
||||
int val = atomic_read(&lock->val);
|
||||
|
||||
for (;;) {
|
||||
int old, new;
|
||||
|
||||
if (val & _Q_LOCKED_MASK)
|
||||
break;
|
||||
|
||||
/*
|
||||
* Try to clear pending bit & set locked bit
|
||||
*/
|
||||
old = val;
|
||||
new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL;
|
||||
val = atomic_cmpxchg(&lock->val, old, new);
|
||||
|
||||
if (val == old)
|
||||
return 1;
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
#endif /* _Q_PENDING_BITS == 8 */
|
||||
|
||||
/*
|
||||
* Include queued spinlock statistics code
|
||||
*/
|
||||
#include "qspinlock_stat.h"
|
||||
|
||||
/*
|
||||
* Lock and MCS node addresses hash table for fast lookup
|
||||
*
|
||||
@ -100,10 +202,13 @@ static struct qspinlock **pv_hash(struct qspinlock *lock, struct pv_node *node)
|
||||
{
|
||||
unsigned long offset, hash = hash_ptr(lock, pv_lock_hash_bits);
|
||||
struct pv_hash_entry *he;
|
||||
int hopcnt = 0;
|
||||
|
||||
for_each_hash_entry(he, offset, hash) {
|
||||
hopcnt++;
|
||||
if (!cmpxchg(&he->lock, NULL, lock)) {
|
||||
WRITE_ONCE(he->node, node);
|
||||
qstat_hop(hopcnt);
|
||||
return &he->lock;
|
||||
}
|
||||
}
|
||||
@ -143,6 +248,20 @@ static struct pv_node *pv_unhash(struct qspinlock *lock)
|
||||
BUG();
|
||||
}
|
||||
|
||||
/*
|
||||
* Return true if when it is time to check the previous node which is not
|
||||
* in a running state.
|
||||
*/
|
||||
static inline bool
|
||||
pv_wait_early(struct pv_node *prev, int loop)
|
||||
{
|
||||
|
||||
if ((loop & PV_PREV_CHECK_MASK) != 0)
|
||||
return false;
|
||||
|
||||
return READ_ONCE(prev->state) != vcpu_running;
|
||||
}
|
||||
|
||||
/*
|
||||
* Initialize the PV part of the mcs_spinlock node.
|
||||
*/
|
||||
@ -161,15 +280,23 @@ static void pv_init_node(struct mcs_spinlock *node)
|
||||
* pv_kick_node() is used to set _Q_SLOW_VAL and fill in hash table on its
|
||||
* behalf.
|
||||
*/
|
||||
static void pv_wait_node(struct mcs_spinlock *node)
|
||||
static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
|
||||
{
|
||||
struct pv_node *pn = (struct pv_node *)node;
|
||||
struct pv_node *pp = (struct pv_node *)prev;
|
||||
int waitcnt = 0;
|
||||
int loop;
|
||||
bool wait_early;
|
||||
|
||||
for (;;) {
|
||||
for (loop = SPIN_THRESHOLD; loop; loop--) {
|
||||
/* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */
|
||||
for (;; waitcnt++) {
|
||||
for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
|
||||
if (READ_ONCE(node->locked))
|
||||
return;
|
||||
if (pv_wait_early(pp, loop)) {
|
||||
wait_early = true;
|
||||
break;
|
||||
}
|
||||
cpu_relax();
|
||||
}
|
||||
|
||||
@ -184,12 +311,17 @@ static void pv_wait_node(struct mcs_spinlock *node)
|
||||
*/
|
||||
smp_store_mb(pn->state, vcpu_halted);
|
||||
|
||||
if (!READ_ONCE(node->locked))
|
||||
if (!READ_ONCE(node->locked)) {
|
||||
qstat_inc(qstat_pv_wait_node, true);
|
||||
qstat_inc(qstat_pv_wait_again, waitcnt);
|
||||
qstat_inc(qstat_pv_wait_early, wait_early);
|
||||
pv_wait(&pn->state, vcpu_halted);
|
||||
}
|
||||
|
||||
/*
|
||||
* If pv_kick_node() changed us to vcpu_hashed, retain that value
|
||||
* so that pv_wait_head() knows to not also try to hash this lock.
|
||||
* If pv_kick_node() changed us to vcpu_hashed, retain that
|
||||
* value so that pv_wait_head_or_lock() knows to not also try
|
||||
* to hash this lock.
|
||||
*/
|
||||
cmpxchg(&pn->state, vcpu_halted, vcpu_running);
|
||||
|
||||
@ -200,6 +332,7 @@ static void pv_wait_node(struct mcs_spinlock *node)
|
||||
* So it is better to spin for a while in the hope that the
|
||||
* MCS lock will be released soon.
|
||||
*/
|
||||
qstat_inc(qstat_pv_spurious_wakeup, !READ_ONCE(node->locked));
|
||||
}
|
||||
|
||||
/*
|
||||
@ -212,8 +345,9 @@ static void pv_wait_node(struct mcs_spinlock *node)
|
||||
/*
|
||||
* Called after setting next->locked = 1 when we're the lock owner.
|
||||
*
|
||||
* Instead of waking the waiters stuck in pv_wait_node() advance their state such
|
||||
* that they're waiting in pv_wait_head(), this avoids a wake/sleep cycle.
|
||||
* Instead of waking the waiters stuck in pv_wait_node() advance their state
|
||||
* such that they're waiting in pv_wait_head_or_lock(), this avoids a
|
||||
* wake/sleep cycle.
|
||||
*/
|
||||
static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
{
|
||||
@ -242,14 +376,19 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
}
|
||||
|
||||
/*
|
||||
* Wait for l->locked to become clear; halt the vcpu after a short spin.
|
||||
* Wait for l->locked to become clear and acquire the lock;
|
||||
* halt the vcpu after a short spin.
|
||||
* __pv_queued_spin_unlock() will wake us.
|
||||
*
|
||||
* The current value of the lock will be returned for additional processing.
|
||||
*/
|
||||
static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
static u32
|
||||
pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
{
|
||||
struct pv_node *pn = (struct pv_node *)node;
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
struct qspinlock **lp = NULL;
|
||||
int waitcnt = 0;
|
||||
int loop;
|
||||
|
||||
/*
|
||||
@ -259,12 +398,25 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
if (READ_ONCE(pn->state) == vcpu_hashed)
|
||||
lp = (struct qspinlock **)1;
|
||||
|
||||
for (;;) {
|
||||
for (;; waitcnt++) {
|
||||
/*
|
||||
* Set correct vCPU state to be used by queue node wait-early
|
||||
* mechanism.
|
||||
*/
|
||||
WRITE_ONCE(pn->state, vcpu_running);
|
||||
|
||||
/*
|
||||
* Set the pending bit in the active lock spinning loop to
|
||||
* disable lock stealing before attempting to acquire the lock.
|
||||
*/
|
||||
set_pending(lock);
|
||||
for (loop = SPIN_THRESHOLD; loop; loop--) {
|
||||
if (!READ_ONCE(l->locked))
|
||||
return;
|
||||
if (trylock_clear_pending(lock))
|
||||
goto gotlock;
|
||||
cpu_relax();
|
||||
}
|
||||
clear_pending(lock);
|
||||
|
||||
|
||||
if (!lp) { /* ONCE */
|
||||
lp = pv_hash(lock, pn);
|
||||
@ -280,51 +432,50 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
|
||||
*
|
||||
* Matches the smp_rmb() in __pv_queued_spin_unlock().
|
||||
*/
|
||||
if (!cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL)) {
|
||||
if (xchg(&l->locked, _Q_SLOW_VAL) == 0) {
|
||||
/*
|
||||
* The lock is free and _Q_SLOW_VAL has never
|
||||
* been set. Therefore we need to unhash before
|
||||
* getting the lock.
|
||||
* The lock was free and now we own the lock.
|
||||
* Change the lock value back to _Q_LOCKED_VAL
|
||||
* and unhash the table.
|
||||
*/
|
||||
WRITE_ONCE(l->locked, _Q_LOCKED_VAL);
|
||||
WRITE_ONCE(*lp, NULL);
|
||||
return;
|
||||
goto gotlock;
|
||||
}
|
||||
}
|
||||
WRITE_ONCE(pn->state, vcpu_halted);
|
||||
qstat_inc(qstat_pv_wait_head, true);
|
||||
qstat_inc(qstat_pv_wait_again, waitcnt);
|
||||
pv_wait(&l->locked, _Q_SLOW_VAL);
|
||||
|
||||
/*
|
||||
* The unlocker should have freed the lock before kicking the
|
||||
* CPU. So if the lock is still not free, it is a spurious
|
||||
* wakeup and so the vCPU should wait again after spinning for
|
||||
* a while.
|
||||
* wakeup or another vCPU has stolen the lock. The current
|
||||
* vCPU should spin again.
|
||||
*/
|
||||
qstat_inc(qstat_pv_spurious_wakeup, READ_ONCE(l->locked));
|
||||
}
|
||||
|
||||
/*
|
||||
* Lock is unlocked now; the caller will acquire it without waiting.
|
||||
* As with pv_wait_node() we rely on the caller to do a load-acquire
|
||||
* for us.
|
||||
* The cmpxchg() or xchg() call before coming here provides the
|
||||
* acquire semantics for locking. The dummy ORing of _Q_LOCKED_VAL
|
||||
* here is to indicate to the compiler that the value will always
|
||||
* be nozero to enable better code optimization.
|
||||
*/
|
||||
gotlock:
|
||||
return (u32)(atomic_read(&lock->val) | _Q_LOCKED_VAL);
|
||||
}
|
||||
|
||||
/*
|
||||
* PV version of the unlock function to be used in stead of
|
||||
* queued_spin_unlock().
|
||||
* PV versions of the unlock fastpath and slowpath functions to be used
|
||||
* instead of queued_spin_unlock().
|
||||
*/
|
||||
__visible void __pv_queued_spin_unlock(struct qspinlock *lock)
|
||||
__visible void
|
||||
__pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
struct pv_node *node;
|
||||
u8 locked;
|
||||
|
||||
/*
|
||||
* We must not unlock if SLOW, because in that case we must first
|
||||
* unhash. Otherwise it would be possible to have multiple @lock
|
||||
* entries, which would be BAD.
|
||||
*/
|
||||
locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
|
||||
if (likely(locked == _Q_LOCKED_VAL))
|
||||
return;
|
||||
|
||||
if (unlikely(locked != _Q_SLOW_VAL)) {
|
||||
WARN(!debug_locks_silent,
|
||||
@ -338,7 +489,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
|
||||
* so we need a barrier to order the read of the node data in
|
||||
* pv_unhash *after* we've read the lock being _Q_SLOW_VAL.
|
||||
*
|
||||
* Matches the cmpxchg() in pv_wait_head() setting _Q_SLOW_VAL.
|
||||
* Matches the cmpxchg() in pv_wait_head_or_lock() setting _Q_SLOW_VAL.
|
||||
*/
|
||||
smp_rmb();
|
||||
|
||||
@ -361,14 +512,35 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
|
||||
* vCPU is harmless other than the additional latency in completing
|
||||
* the unlock.
|
||||
*/
|
||||
qstat_inc(qstat_pv_kick_unlock, true);
|
||||
pv_kick(node->cpu);
|
||||
}
|
||||
|
||||
/*
|
||||
* Include the architecture specific callee-save thunk of the
|
||||
* __pv_queued_spin_unlock(). This thunk is put together with
|
||||
* __pv_queued_spin_unlock() near the top of the file to make sure
|
||||
* that the callee-save thunk and the real unlock function are close
|
||||
* to each other sharing consecutive instruction cachelines.
|
||||
* __pv_queued_spin_unlock() to make the callee-save thunk and the real unlock
|
||||
* function close to each other sharing consecutive instruction cachelines.
|
||||
* Alternatively, architecture specific version of __pv_queued_spin_unlock()
|
||||
* can be defined.
|
||||
*/
|
||||
#include <asm/qspinlock_paravirt.h>
|
||||
|
||||
#ifndef __pv_queued_spin_unlock
|
||||
__visible void __pv_queued_spin_unlock(struct qspinlock *lock)
|
||||
{
|
||||
struct __qspinlock *l = (void *)lock;
|
||||
u8 locked;
|
||||
|
||||
/*
|
||||
* We must not unlock if SLOW, because in that case we must first
|
||||
* unhash. Otherwise it would be possible to have multiple @lock
|
||||
* entries, which would be BAD.
|
||||
*/
|
||||
locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
|
||||
if (likely(locked == _Q_LOCKED_VAL))
|
||||
return;
|
||||
|
||||
__pv_queued_spin_unlock_slowpath(lock, locked);
|
||||
}
|
||||
#endif /* __pv_queued_spin_unlock */
|
||||
|
300
kernel/locking/qspinlock_stat.h
Normal file
300
kernel/locking/qspinlock_stat.h
Normal file
@ -0,0 +1,300 @@
|
||||
/*
|
||||
* This program is free software; you can redistribute it and/or modify
|
||||
* it under the terms of the GNU General Public License as published by
|
||||
* the Free Software Foundation; either version 2 of the License, or
|
||||
* (at your option) any later version.
|
||||
*
|
||||
* This program is distributed in the hope that it will be useful,
|
||||
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
* GNU General Public License for more details.
|
||||
*
|
||||
* Authors: Waiman Long <waiman.long@hpe.com>
|
||||
*/
|
||||
|
||||
/*
|
||||
* When queued spinlock statistical counters are enabled, the following
|
||||
* debugfs files will be created for reporting the counter values:
|
||||
*
|
||||
* <debugfs>/qlockstat/
|
||||
* pv_hash_hops - average # of hops per hashing operation
|
||||
* pv_kick_unlock - # of vCPU kicks issued at unlock time
|
||||
* pv_kick_wake - # of vCPU kicks used for computing pv_latency_wake
|
||||
* pv_latency_kick - average latency (ns) of vCPU kick operation
|
||||
* pv_latency_wake - average latency (ns) from vCPU kick to wakeup
|
||||
* pv_lock_stealing - # of lock stealing operations
|
||||
* pv_spurious_wakeup - # of spurious wakeups
|
||||
* pv_wait_again - # of vCPU wait's that happened after a vCPU kick
|
||||
* pv_wait_early - # of early vCPU wait's
|
||||
* pv_wait_head - # of vCPU wait's at the queue head
|
||||
* pv_wait_node - # of vCPU wait's at a non-head queue node
|
||||
*
|
||||
* Writing to the "reset_counters" file will reset all the above counter
|
||||
* values.
|
||||
*
|
||||
* These statistical counters are implemented as per-cpu variables which are
|
||||
* summed and computed whenever the corresponding debugfs files are read. This
|
||||
* minimizes added overhead making the counters usable even in a production
|
||||
* environment.
|
||||
*
|
||||
* There may be slight difference between pv_kick_wake and pv_kick_unlock.
|
||||
*/
|
||||
enum qlock_stats {
|
||||
qstat_pv_hash_hops,
|
||||
qstat_pv_kick_unlock,
|
||||
qstat_pv_kick_wake,
|
||||
qstat_pv_latency_kick,
|
||||
qstat_pv_latency_wake,
|
||||
qstat_pv_lock_stealing,
|
||||
qstat_pv_spurious_wakeup,
|
||||
qstat_pv_wait_again,
|
||||
qstat_pv_wait_early,
|
||||
qstat_pv_wait_head,
|
||||
qstat_pv_wait_node,
|
||||
qstat_num, /* Total number of statistical counters */
|
||||
qstat_reset_cnts = qstat_num,
|
||||
};
|
||||
|
||||
#ifdef CONFIG_QUEUED_LOCK_STAT
|
||||
/*
|
||||
* Collect pvqspinlock statistics
|
||||
*/
|
||||
#include <linux/debugfs.h>
|
||||
#include <linux/sched.h>
|
||||
#include <linux/fs.h>
|
||||
|
||||
static const char * const qstat_names[qstat_num + 1] = {
|
||||
[qstat_pv_hash_hops] = "pv_hash_hops",
|
||||
[qstat_pv_kick_unlock] = "pv_kick_unlock",
|
||||
[qstat_pv_kick_wake] = "pv_kick_wake",
|
||||
[qstat_pv_spurious_wakeup] = "pv_spurious_wakeup",
|
||||
[qstat_pv_latency_kick] = "pv_latency_kick",
|
||||
[qstat_pv_latency_wake] = "pv_latency_wake",
|
||||
[qstat_pv_lock_stealing] = "pv_lock_stealing",
|
||||
[qstat_pv_wait_again] = "pv_wait_again",
|
||||
[qstat_pv_wait_early] = "pv_wait_early",
|
||||
[qstat_pv_wait_head] = "pv_wait_head",
|
||||
[qstat_pv_wait_node] = "pv_wait_node",
|
||||
[qstat_reset_cnts] = "reset_counters",
|
||||
};
|
||||
|
||||
/*
|
||||
* Per-cpu counters
|
||||
*/
|
||||
static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]);
|
||||
static DEFINE_PER_CPU(u64, pv_kick_time);
|
||||
|
||||
/*
|
||||
* Function to read and return the qlock statistical counter values
|
||||
*
|
||||
* The following counters are handled specially:
|
||||
* 1. qstat_pv_latency_kick
|
||||
* Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
|
||||
* 2. qstat_pv_latency_wake
|
||||
* Average wake latency (ns) = pv_latency_wake/pv_kick_wake
|
||||
* 3. qstat_pv_hash_hops
|
||||
* Average hops/hash = pv_hash_hops/pv_kick_unlock
|
||||
*/
|
||||
static ssize_t qstat_read(struct file *file, char __user *user_buf,
|
||||
size_t count, loff_t *ppos)
|
||||
{
|
||||
char buf[64];
|
||||
int cpu, counter, len;
|
||||
u64 stat = 0, kicks = 0;
|
||||
|
||||
/*
|
||||
* Get the counter ID stored in file->f_inode->i_private
|
||||
*/
|
||||
if (!file->f_inode) {
|
||||
WARN_ON_ONCE(1);
|
||||
return -EBADF;
|
||||
}
|
||||
counter = (long)(file->f_inode->i_private);
|
||||
|
||||
if (counter >= qstat_num)
|
||||
return -EBADF;
|
||||
|
||||
for_each_possible_cpu(cpu) {
|
||||
stat += per_cpu(qstats[counter], cpu);
|
||||
/*
|
||||
* Need to sum additional counter for some of them
|
||||
*/
|
||||
switch (counter) {
|
||||
|
||||
case qstat_pv_latency_kick:
|
||||
case qstat_pv_hash_hops:
|
||||
kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
|
||||
break;
|
||||
|
||||
case qstat_pv_latency_wake:
|
||||
kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
if (counter == qstat_pv_hash_hops) {
|
||||
u64 frac;
|
||||
|
||||
frac = 100ULL * do_div(stat, kicks);
|
||||
frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
|
||||
|
||||
/*
|
||||
* Return a X.XX decimal number
|
||||
*/
|
||||
len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac);
|
||||
} else {
|
||||
/*
|
||||
* Round to the nearest ns
|
||||
*/
|
||||
if ((counter == qstat_pv_latency_kick) ||
|
||||
(counter == qstat_pv_latency_wake)) {
|
||||
stat = 0;
|
||||
if (kicks)
|
||||
stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
|
||||
}
|
||||
len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
|
||||
}
|
||||
|
||||
return simple_read_from_buffer(user_buf, count, ppos, buf, len);
|
||||
}
|
||||
|
||||
/*
|
||||
* Function to handle write request
|
||||
*
|
||||
* When counter = reset_cnts, reset all the counter values.
|
||||
* Since the counter updates aren't atomic, the resetting is done twice
|
||||
* to make sure that the counters are very likely to be all cleared.
|
||||
*/
|
||||
static ssize_t qstat_write(struct file *file, const char __user *user_buf,
|
||||
size_t count, loff_t *ppos)
|
||||
{
|
||||
int cpu;
|
||||
|
||||
/*
|
||||
* Get the counter ID stored in file->f_inode->i_private
|
||||
*/
|
||||
if (!file->f_inode) {
|
||||
WARN_ON_ONCE(1);
|
||||
return -EBADF;
|
||||
}
|
||||
if ((long)(file->f_inode->i_private) != qstat_reset_cnts)
|
||||
return count;
|
||||
|
||||
for_each_possible_cpu(cpu) {
|
||||
int i;
|
||||
unsigned long *ptr = per_cpu_ptr(qstats, cpu);
|
||||
|
||||
for (i = 0 ; i < qstat_num; i++)
|
||||
WRITE_ONCE(ptr[i], 0);
|
||||
for (i = 0 ; i < qstat_num; i++)
|
||||
WRITE_ONCE(ptr[i], 0);
|
||||
}
|
||||
return count;
|
||||
}
|
||||
|
||||
/*
|
||||
* Debugfs data structures
|
||||
*/
|
||||
static const struct file_operations fops_qstat = {
|
||||
.read = qstat_read,
|
||||
.write = qstat_write,
|
||||
.llseek = default_llseek,
|
||||
};
|
||||
|
||||
/*
|
||||
* Initialize debugfs for the qspinlock statistical counters
|
||||
*/
|
||||
static int __init init_qspinlock_stat(void)
|
||||
{
|
||||
struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
|
||||
int i;
|
||||
|
||||
if (!d_qstat) {
|
||||
pr_warn("Could not create 'qlockstat' debugfs directory\n");
|
||||
return 0;
|
||||
}
|
||||
|
||||
/*
|
||||
* Create the debugfs files
|
||||
*
|
||||
* As reading from and writing to the stat files can be slow, only
|
||||
* root is allowed to do the read/write to limit impact to system
|
||||
* performance.
|
||||
*/
|
||||
for (i = 0; i < qstat_num; i++)
|
||||
debugfs_create_file(qstat_names[i], 0400, d_qstat,
|
||||
(void *)(long)i, &fops_qstat);
|
||||
|
||||
debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
|
||||
(void *)(long)qstat_reset_cnts, &fops_qstat);
|
||||
return 0;
|
||||
}
|
||||
fs_initcall(init_qspinlock_stat);
|
||||
|
||||
/*
|
||||
* Increment the PV qspinlock statistical counters
|
||||
*/
|
||||
static inline void qstat_inc(enum qlock_stats stat, bool cond)
|
||||
{
|
||||
if (cond)
|
||||
this_cpu_inc(qstats[stat]);
|
||||
}
|
||||
|
||||
/*
|
||||
* PV hash hop count
|
||||
*/
|
||||
static inline void qstat_hop(int hopcnt)
|
||||
{
|
||||
this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt);
|
||||
}
|
||||
|
||||
/*
|
||||
* Replacement function for pv_kick()
|
||||
*/
|
||||
static inline void __pv_kick(int cpu)
|
||||
{
|
||||
u64 start = sched_clock();
|
||||
|
||||
per_cpu(pv_kick_time, cpu) = start;
|
||||
pv_kick(cpu);
|
||||
this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start);
|
||||
}
|
||||
|
||||
/*
|
||||
* Replacement function for pv_wait()
|
||||
*/
|
||||
static inline void __pv_wait(u8 *ptr, u8 val)
|
||||
{
|
||||
u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
|
||||
|
||||
*pkick_time = 0;
|
||||
pv_wait(ptr, val);
|
||||
if (*pkick_time) {
|
||||
this_cpu_add(qstats[qstat_pv_latency_wake],
|
||||
sched_clock() - *pkick_time);
|
||||
qstat_inc(qstat_pv_kick_wake, true);
|
||||
}
|
||||
}
|
||||
|
||||
#define pv_kick(c) __pv_kick(c)
|
||||
#define pv_wait(p, v) __pv_wait(p, v)
|
||||
|
||||
/*
|
||||
* PV unfair trylock count tracking function
|
||||
*/
|
||||
static inline int qstat_spin_steal_lock(struct qspinlock *lock)
|
||||
{
|
||||
int ret = pv_queued_spin_steal_lock(lock);
|
||||
|
||||
qstat_inc(qstat_pv_lock_stealing, ret);
|
||||
return ret;
|
||||
}
|
||||
#undef queued_spin_trylock
|
||||
#define queued_spin_trylock(l) qstat_spin_steal_lock(l)
|
||||
|
||||
#else /* CONFIG_QUEUED_LOCK_STAT */
|
||||
|
||||
static inline void qstat_inc(enum qlock_stats stat, bool cond) { }
|
||||
static inline void qstat_hop(int hopcnt) { }
|
||||
|
||||
#endif /* CONFIG_QUEUED_LOCK_STAT */
|
@ -1905,6 +1905,97 @@ static void ttwu_queue(struct task_struct *p, int cpu)
|
||||
raw_spin_unlock(&rq->lock);
|
||||
}
|
||||
|
||||
/*
|
||||
* Notes on Program-Order guarantees on SMP systems.
|
||||
*
|
||||
* MIGRATION
|
||||
*
|
||||
* The basic program-order guarantee on SMP systems is that when a task [t]
|
||||
* migrates, all its activity on its old cpu [c0] happens-before any subsequent
|
||||
* execution on its new cpu [c1].
|
||||
*
|
||||
* For migration (of runnable tasks) this is provided by the following means:
|
||||
*
|
||||
* A) UNLOCK of the rq(c0)->lock scheduling out task t
|
||||
* B) migration for t is required to synchronize *both* rq(c0)->lock and
|
||||
* rq(c1)->lock (if not at the same time, then in that order).
|
||||
* C) LOCK of the rq(c1)->lock scheduling in task
|
||||
*
|
||||
* Transitivity guarantees that B happens after A and C after B.
|
||||
* Note: we only require RCpc transitivity.
|
||||
* Note: the cpu doing B need not be c0 or c1
|
||||
*
|
||||
* Example:
|
||||
*
|
||||
* CPU0 CPU1 CPU2
|
||||
*
|
||||
* LOCK rq(0)->lock
|
||||
* sched-out X
|
||||
* sched-in Y
|
||||
* UNLOCK rq(0)->lock
|
||||
*
|
||||
* LOCK rq(0)->lock // orders against CPU0
|
||||
* dequeue X
|
||||
* UNLOCK rq(0)->lock
|
||||
*
|
||||
* LOCK rq(1)->lock
|
||||
* enqueue X
|
||||
* UNLOCK rq(1)->lock
|
||||
*
|
||||
* LOCK rq(1)->lock // orders against CPU2
|
||||
* sched-out Z
|
||||
* sched-in X
|
||||
* UNLOCK rq(1)->lock
|
||||
*
|
||||
*
|
||||
* BLOCKING -- aka. SLEEP + WAKEUP
|
||||
*
|
||||
* For blocking we (obviously) need to provide the same guarantee as for
|
||||
* migration. However the means are completely different as there is no lock
|
||||
* chain to provide order. Instead we do:
|
||||
*
|
||||
* 1) smp_store_release(X->on_cpu, 0)
|
||||
* 2) smp_cond_acquire(!X->on_cpu)
|
||||
*
|
||||
* Example:
|
||||
*
|
||||
* CPU0 (schedule) CPU1 (try_to_wake_up) CPU2 (schedule)
|
||||
*
|
||||
* LOCK rq(0)->lock LOCK X->pi_lock
|
||||
* dequeue X
|
||||
* sched-out X
|
||||
* smp_store_release(X->on_cpu, 0);
|
||||
*
|
||||
* smp_cond_acquire(!X->on_cpu);
|
||||
* X->state = WAKING
|
||||
* set_task_cpu(X,2)
|
||||
*
|
||||
* LOCK rq(2)->lock
|
||||
* enqueue X
|
||||
* X->state = RUNNING
|
||||
* UNLOCK rq(2)->lock
|
||||
*
|
||||
* LOCK rq(2)->lock // orders against CPU1
|
||||
* sched-out Z
|
||||
* sched-in X
|
||||
* UNLOCK rq(2)->lock
|
||||
*
|
||||
* UNLOCK X->pi_lock
|
||||
* UNLOCK rq(0)->lock
|
||||
*
|
||||
*
|
||||
* However; for wakeups there is a second guarantee we must provide, namely we
|
||||
* must observe the state that lead to our wakeup. That is, not only must our
|
||||
* task observe its own prior state, it must also observe the stores prior to
|
||||
* its wakeup.
|
||||
*
|
||||
* This means that any means of doing remote wakeups must order the CPU doing
|
||||
* the wakeup against the CPU the task is going to end up running on. This,
|
||||
* however, is already required for the regular Program-Order guarantee above,
|
||||
* since the waking CPU is the one issueing the ACQUIRE (smp_cond_acquire).
|
||||
*
|
||||
*/
|
||||
|
||||
/**
|
||||
* try_to_wake_up - wake up a thread
|
||||
* @p: the thread to be awakened
|
||||
@ -1968,19 +2059,13 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
|
||||
/*
|
||||
* If the owning (remote) cpu is still in the middle of schedule() with
|
||||
* this task as prev, wait until its done referencing the task.
|
||||
*/
|
||||
while (p->on_cpu)
|
||||
cpu_relax();
|
||||
/*
|
||||
* Combined with the control dependency above, we have an effective
|
||||
* smp_load_acquire() without the need for full barriers.
|
||||
*
|
||||
* Pairs with the smp_store_release() in finish_lock_switch().
|
||||
*
|
||||
* This ensures that tasks getting woken will be fully ordered against
|
||||
* their previous state and preserve Program Order.
|
||||
*/
|
||||
smp_rmb();
|
||||
smp_cond_acquire(!p->on_cpu);
|
||||
|
||||
p->sched_contributes_to_load = !!task_contributes_to_load(p);
|
||||
p->state = TASK_WAKING;
|
||||
|
@ -1076,7 +1076,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
|
||||
* In particular, the load of prev->state in finish_task_switch() must
|
||||
* happen before this.
|
||||
*
|
||||
* Pairs with the control dependency and rmb in try_to_wake_up().
|
||||
* Pairs with the smp_cond_acquire() in try_to_wake_up().
|
||||
*/
|
||||
smp_store_release(&prev->on_cpu, 0);
|
||||
#endif
|
||||
|
@ -27,6 +27,65 @@ do { \
|
||||
(unsigned long long)r); \
|
||||
} while (0)
|
||||
|
||||
/*
|
||||
* Test for a atomic operation family,
|
||||
* @test should be a macro accepting parameters (bit, op, ...)
|
||||
*/
|
||||
|
||||
#define FAMILY_TEST(test, bit, op, args...) \
|
||||
do { \
|
||||
test(bit, op, ##args); \
|
||||
test(bit, op##_acquire, ##args); \
|
||||
test(bit, op##_release, ##args); \
|
||||
test(bit, op##_relaxed, ##args); \
|
||||
} while (0)
|
||||
|
||||
#define TEST_RETURN(bit, op, c_op, val) \
|
||||
do { \
|
||||
atomic##bit##_set(&v, v0); \
|
||||
r = v0; \
|
||||
r c_op val; \
|
||||
BUG_ON(atomic##bit##_##op(val, &v) != r); \
|
||||
BUG_ON(atomic##bit##_read(&v) != r); \
|
||||
} while (0)
|
||||
|
||||
#define RETURN_FAMILY_TEST(bit, op, c_op, val) \
|
||||
do { \
|
||||
FAMILY_TEST(TEST_RETURN, bit, op, c_op, val); \
|
||||
} while (0)
|
||||
|
||||
#define TEST_ARGS(bit, op, init, ret, expect, args...) \
|
||||
do { \
|
||||
atomic##bit##_set(&v, init); \
|
||||
BUG_ON(atomic##bit##_##op(&v, ##args) != ret); \
|
||||
BUG_ON(atomic##bit##_read(&v) != expect); \
|
||||
} while (0)
|
||||
|
||||
#define XCHG_FAMILY_TEST(bit, init, new) \
|
||||
do { \
|
||||
FAMILY_TEST(TEST_ARGS, bit, xchg, init, init, new, new); \
|
||||
} while (0)
|
||||
|
||||
#define CMPXCHG_FAMILY_TEST(bit, init, new, wrong) \
|
||||
do { \
|
||||
FAMILY_TEST(TEST_ARGS, bit, cmpxchg, \
|
||||
init, init, new, init, new); \
|
||||
FAMILY_TEST(TEST_ARGS, bit, cmpxchg, \
|
||||
init, init, init, wrong, new); \
|
||||
} while (0)
|
||||
|
||||
#define INC_RETURN_FAMILY_TEST(bit, i) \
|
||||
do { \
|
||||
FAMILY_TEST(TEST_ARGS, bit, inc_return, \
|
||||
i, (i) + one, (i) + one); \
|
||||
} while (0)
|
||||
|
||||
#define DEC_RETURN_FAMILY_TEST(bit, i) \
|
||||
do { \
|
||||
FAMILY_TEST(TEST_ARGS, bit, dec_return, \
|
||||
i, (i) - one, (i) - one); \
|
||||
} while (0)
|
||||
|
||||
static __init void test_atomic(void)
|
||||
{
|
||||
int v0 = 0xaaa31337;
|
||||
@ -45,6 +104,18 @@ static __init void test_atomic(void)
|
||||
TEST(, and, &=, v1);
|
||||
TEST(, xor, ^=, v1);
|
||||
TEST(, andnot, &= ~, v1);
|
||||
|
||||
RETURN_FAMILY_TEST(, add_return, +=, onestwos);
|
||||
RETURN_FAMILY_TEST(, add_return, +=, -one);
|
||||
RETURN_FAMILY_TEST(, sub_return, -=, onestwos);
|
||||
RETURN_FAMILY_TEST(, sub_return, -=, -one);
|
||||
|
||||
INC_RETURN_FAMILY_TEST(, v0);
|
||||
DEC_RETURN_FAMILY_TEST(, v0);
|
||||
|
||||
XCHG_FAMILY_TEST(, v0, v1);
|
||||
CMPXCHG_FAMILY_TEST(, v0, v1, onestwos);
|
||||
|
||||
}
|
||||
|
||||
#define INIT(c) do { atomic64_set(&v, c); r = c; } while (0)
|
||||
@ -74,59 +145,26 @@ static __init void test_atomic64(void)
|
||||
TEST(64, xor, ^=, v1);
|
||||
TEST(64, andnot, &= ~, v1);
|
||||
|
||||
INIT(v0);
|
||||
r += onestwos;
|
||||
BUG_ON(atomic64_add_return(onestwos, &v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
r += -one;
|
||||
BUG_ON(atomic64_add_return(-one, &v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
r -= onestwos;
|
||||
BUG_ON(atomic64_sub_return(onestwos, &v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
r -= -one;
|
||||
BUG_ON(atomic64_sub_return(-one, &v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
RETURN_FAMILY_TEST(64, add_return, +=, onestwos);
|
||||
RETURN_FAMILY_TEST(64, add_return, +=, -one);
|
||||
RETURN_FAMILY_TEST(64, sub_return, -=, onestwos);
|
||||
RETURN_FAMILY_TEST(64, sub_return, -=, -one);
|
||||
|
||||
INIT(v0);
|
||||
atomic64_inc(&v);
|
||||
r += one;
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
r += one;
|
||||
BUG_ON(atomic64_inc_return(&v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
atomic64_dec(&v);
|
||||
r -= one;
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
r -= one;
|
||||
BUG_ON(atomic64_dec_return(&v) != r);
|
||||
BUG_ON(v.counter != r);
|
||||
INC_RETURN_FAMILY_TEST(64, v0);
|
||||
DEC_RETURN_FAMILY_TEST(64, v0);
|
||||
|
||||
INIT(v0);
|
||||
BUG_ON(atomic64_xchg(&v, v1) != v0);
|
||||
r = v1;
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
BUG_ON(atomic64_cmpxchg(&v, v0, v1) != v0);
|
||||
r = v1;
|
||||
BUG_ON(v.counter != r);
|
||||
|
||||
INIT(v0);
|
||||
BUG_ON(atomic64_cmpxchg(&v, v2, v1) != v0);
|
||||
BUG_ON(v.counter != r);
|
||||
XCHG_FAMILY_TEST(64, v0, v1);
|
||||
CMPXCHG_FAMILY_TEST(64, v0, v1, v2);
|
||||
|
||||
INIT(v0);
|
||||
BUG_ON(atomic64_add_unless(&v, one, v0));
|
||||
|
Loading…
Reference in New Issue
Block a user