在 2023/7/31 10:33, guoren@xxxxxxxxxx 写道: > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > The arch_spin_value_unlocked would cause an unnecessary memory > access to the contended value. Although it won't cause a significant > performance gap in most architectures, the arch_spin_value_unlocked > argument contains enough information. Thus, remove unnecessary > atomic_read in arch_spin_value_unlocked(). > > The caller of arch_spin_value_unlocked() could benefit from this > change. Currently, the only caller is lockref. > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> > Cc: Waiman Long <longman@xxxxxxxxxx> > Cc: David Laight <David.Laight@xxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > --- > Changelog > V2: > - Fixup commit log with Waiman advice. > - Add Waiman comment in the commit msg. > --- > include/asm-generic/spinlock.h | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > > diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h > index fdfebcb050f4..90803a826ba0 100644 > --- a/include/asm-generic/spinlock.h > +++ b/include/asm-generic/spinlock.h > @@ -68,11 +68,18 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) > smp_store_release(ptr, (u16)val + 1); > } > > +static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) > +{ > + u32 val = lock.counter; > + > + return ((val >> 16) == (val & 0xffff)); > +} I do not know much about lock, will it be cached in register without memory access again like READ_ONCE or atomic_read? Regards Bibo Mao > + > static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock) > { > - u32 val = atomic_read(lock); > + arch_spinlock_t val = READ_ONCE(*lock); > > - return ((val >> 16) != (val & 0xffff)); > + return !arch_spin_value_unlocked(val); > } > > static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock) > @@ -82,11 +89,6 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock) > return (s16)((val >> 16) - (val & 0xffff)) > 1; > } > > -static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) > -{ > - return !arch_spin_is_locked(&lock); > -} > - > #include <asm/qrwlock.h> > > #endif /* __ASM_GENERIC_SPINLOCK_H */