On Tue, Dec 16, 2014 at 02:00:40PM +0800, Baoquan He wrote: > In queue_read_lock_slowpath, when writer count becomes 0, we need > increment the read count and get the lock. Then need call > rspin_until_writer_unlock to check again if an incoming writer > steals the lock in the gap. But in rspin_until_writer_unlock > it only checks the writer count, namely low 8 bit of lock->cnts, > no need to subtract the reader count unit specifically. So remove > that subtraction to make it clearer, rspin_until_writer_unlock > just takes the actual lock->cnts as the 2nd argument. > > And also change the code comment in queue_write_lock_slowpath to > make it more exact and explicit. > > Signed-off-by: Baoquan He <b...@redhat.com> > --- > kernel/locking/qrwlock.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c > index f956ede..ae66c10 100644 > --- a/kernel/locking/qrwlock.c > +++ b/kernel/locking/qrwlock.c > @@ -76,7 +76,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock) > while (atomic_read(&lock->cnts) & _QW_WMASK) > cpu_relax_lowlatency(); > > - cnts = atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS; > + cnts = atomic_add_return(_QR_BIAS, &lock->cnts); > rspin_until_writer_unlock(lock, cnts);
Did you actually look at the ASM generated? I suspect your change makes it bigger. -- 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/
