Messages in this thread | | | Subject | Re: [PATCH v3] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write | From | Jason Low <> | Date | Tue, 28 Apr 2015 10:59:18 -0700 |
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On Tue, 2015-04-28 at 10:50 -0700, Jason Low wrote: > On Tue, 2015-04-28 at 19:17 +0200, Peter Zijlstra wrote: > > > To me it makes more sense to reverse these two branches (identical code > > wise of course) and put the special case first. > > > > Alternatively we could also do something like the below, which to my > > eyes looks a little better still, but I don't care too much. > > > > if (rwsem_has_spinner(sem)) { > > /* > > * comment ... > > */ > > smp_rmb(); > > if (!raw_spin_trylock_irqsave(&sem->wait_lock, flags)) > > return sem; > > goto locked; > > } > > > > raw_spin_lock_irqsave(&sem->wait_lock, flags); > > locked: > > How about putting this into its own function: > > static inline bool __rwsem_wake_acquire_wait_lock(sem) > { > /* > * > * Comments > * > */ > if (unlikely(rwsem_has_spinner(sem))) { > /* > * Comments > */ > smp_rmb(); > if (!raw_spin_trylock_irqsave(&sem->wait_lock, flags)) > return false; > } > > return true; > }
That is, with the raw_spin_lock_irqsave() too :)
static inline bool __rwsem_wake_acquire_wait_lock(sem) { /* * * Comments * */ if (unlikely(rwsem_has_spinner(sem))) { /* * Comments */ smp_rmb(); if (!raw_spin_trylock_irqsave(&sem->wait_lock, flags)) return false;
/* trylock successful */ return true; }
raw_spin_lock_irqsave(&sem->wait_lock, flags); return true; }
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