On 12/8/20 5:07 AM, Peter Zijlstra wrote:
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..
You are right. I forgot to take that out.
- * 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?
That is true. Patch 4 isn't essential for this series. So if you are general OK with the current patchset, I can send out v3 that remove patch 4 and make the your suggested change above.
Cheers, Longman
