Re: [PATCH V2] lglock: add read-preference local-global rwlock

On 03/05, Lai Jiangshan wrote:

On 03/03/13 01:20, Oleg Nesterov wrote:

quoted

On 03/02, Lai Jiangshan wrote:

quoted

+void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
+{
+	switch (__this_cpu_read(*lgrw->reader_refcnt)) {
+	case 1:
+		__this_cpu_write(*lgrw->reader_refcnt, 0);
+		lg_local_unlock(&lgrw->lglock);
+		return;
+	case FALLBACK_BASE:
+		__this_cpu_write(*lgrw->reader_refcnt, 0);
+		read_unlock(&lgrw->fallback_rwlock);
+		rwlock_release(&lg->lock_dep_map, 1, _RET_IP_);

I guess "case 1:" should do rwlock_release() too.

Already do it in "lg_local_unlock(&lgrw->lglock);" before it returns.
(I like reuse old code)

Yes, I was wrong thanks. Another case when I didn't notice that you
re-use the regular lg_ code...

quoted

We need rwlock_acquire_read() even in the fast-path, and this acquire_read
should be paired with rwlock_acquire() in _write_lock(), but it does
spin_acquire(lg->lock_dep_map). Yes, currently this is the same (afaics)
but perhaps fallback_rwlock->dep_map would be more clean.

I can't tell which one is better. I try to use fallback_rwlock->dep_map later.

I am not sure which one should be better too, please check.

Again, I forgot that _write_lock/unlock use lg_global_*() code.

Oleg.