On Fri, Nov 20, 2020 at 11:14:16PM -0500, Waiman Long wrote:
> @@ -1032,40 +901,16 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int
> state, long count)
> *
> * We can take the read lock directly without doing
> * rwsem_optimistic_spin() if the conditions are right.
This comment no longer makes sense..
> - * Also wake up other readers if it is the first reader.
> */
> - if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF)) &&
> - rwsem_no_spinners(sem)) {
> + if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
> rwsem_set_reader_owned(sem);
> lockevent_inc(rwsem_rlock_steal);
> - if (rcnt == 1)
> - goto wake_readers;
> - return sem;
> - }
>
> - /*
> - * Save the current read-owner of rwsem, if available, and the
> - * reader nonspinnable bit.
> - */
> - waiter.last_rowner = owner;
> - if (!(waiter.last_rowner & RWSEM_READER_OWNED))
> - waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
> -
> - if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
> - goto queue;
> -
> - /*
> - * Undo read bias from down_read() and do optimistic spinning.
> - */
> - atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
> - adjustment = 0;
> - if (rwsem_optimistic_spin(sem, false)) {
since we're removing the optimistic spinning entirely on the read side.
Also, I was looking at skipping patch #4, which mucks with the reader
wakeup logic, and afaict this removal doesn't really depend on it.
Or am I missing something?
