On Wed, Jun 04, 2014 at 12:08:29PM -0700, Jason Low wrote: > Upon entering the slowpath in __mutex_lock_common(), we try once more > to acquire the mutex. We only try to acquire it if MUTEX_SHOW_NO_WAITER > (lock->count >= 0) is true in order to avoid using the atomic xchg() > operation whenever it is not necessary. However, we really only need > to try to acquire if the mutex is free (lock->count == 1). > > This patch changes it so that we only try-acquire the mutex upon > entering the slowpath if it is unlocked, rather than if there are > no waiters. This helps further reduce unncessary atomic xchg() > operations. Furthermore, this patch introduces and uses a new > MUTEX_IS_UNLOCKED() macro to improve readbability. > > Signed-off-by: Jason Low <jason.l...@hp.com> > --- > kernel/locking/mutex.c | 10 ++++++---- > 1 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index bc73d33..0925968 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -48,9 +48,10 @@ > > /* > * A negative mutex count indicates that waiters are sleeping waiting for the > - * mutex. > + * mutex, and a count of one indicates the mutex is unlocked. > */ > #define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) > >= 0) > +#define MUTEX_IS_UNLOCKED(mutex) (atomic_read(&(mutex)->count) > == 1)
So I recently saw that MUTEX_SHOW_NO_WAITER thing and cried a little; and now you're adding more of that same nonsense. Please make them inline functions, also can we rename the SHOW_NO_WAITER thing, because its not at all clear to me wtf it does; should it be called: mutex_no_waiters() or somesuch? -- 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/
