asm-generic: ticket-lock: Optimize arch_spin_value_unlocked()
The arch_spin_value_unlocked() of ticket-lock would cause the compiler to generate inefficient asm code in riscv architecture because of unnecessary memory access to the contended value. Before the patch: void lockref_get(struct lockref *lockref) { 78: fd010113 add sp,sp,-48 7c: 02813023 sd s0,32(sp) 80: 02113423 sd ra,40(sp) 84: 03010413 add s0,sp,48 0000000000000088 <.LBB296>: CMPXCHG_LOOP( 88: 00053783 ld a5,0(a0) After the patch: void lockref_get(struct lockref *lockref) { CMPXCHG_LOOP( 78: 00053783 ld a5,0(a0) After the patch, the lockref_get() could get in a fast path instead of the function's prologue. This is because ticket lock complex logic would limit compiler optimization for the spinlock fast path, and qspinlock won't. The caller of arch_spin_value_unlocked() could benefit from this change. Currently, the only caller is lockref. Signed-off-by: Guo Ren <guoren@kernel.org> Signed-off-by: Guo Ren <guoren@linux.alibaba.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Waiman Long <longman@redhat.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20230908154339.3250567-1-guoren@kernel.org
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@ -68,11 +68,18 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
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smp_store_release(ptr, (u16)val + 1);
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smp_store_release(ptr, (u16)val + 1);
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}
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}
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static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
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{
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u32 val = lock.counter;
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return ((val >> 16) == (val & 0xffff));
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}
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static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
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static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
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{
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{
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u32 val = atomic_read(lock);
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arch_spinlock_t val = READ_ONCE(*lock);
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return ((val >> 16) != (val & 0xffff));
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return !arch_spin_value_unlocked(val);
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}
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}
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static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
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static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
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@ -82,11 +89,6 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
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return (s16)((val >> 16) - (val & 0xffff)) > 1;
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return (s16)((val >> 16) - (val & 0xffff)) > 1;
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}
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}
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static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
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{
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return !arch_spin_is_locked(&lock);
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}
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#include <asm/qrwlock.h>
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#include <asm/qrwlock.h>
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#endif /* __ASM_GENERIC_SPINLOCK_H */
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#endif /* __ASM_GENERIC_SPINLOCK_H */
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