Messages in this thread | | | Date | Tue, 8 Dec 2020 11:07:04 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 5/5] locking/rwsem: Remove reader optimistic spinning |
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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?
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