On Wed, 2014-06-04 at 14:47 -0700, Jason Low wrote: > On Wed, 2014-06-04 at 13:28 -0700, Davidlohr Bueso wrote: > > On Wed, 2014-06-04 at 12:08 -0700, Jason Low wrote: > > > In __mutex_trylock_slowpath(), we acquire the wait_lock spinlock, > > > xchg() lock->count with -1, then set lock->count back to 0 if there > > > are no waiters, and return true if the prev lock count was 1. > > > > > > However, if we the mutex is already locked, then there may not be > > ^^ leave that out. > > > > > much point in attempting the above operations. > > > > Isn't this redundant? I mean, if we enter the slowpath its because > > __mutex_fastpath_trylock() already failed so we already know that the > > lock is taken. > > This function is really just used as an alternative method of trylock > for !__HAVE_ARCH_CMPXCHG. In that case, the fastpath can call directly > into the slowpath function, without checking for if the lock is taken.
Ah, ok I hadn't seen that we do this in 32bit x86 and was wondering why the heck we fallback on a slowpath for something like trylock, which should return right away no matter what. I'd suggest explicitly mentioning this in the changelog. Otherwise makes sense now. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
