@@ -237,16 +237,9 @@ void btrfs_tree_lock(struct extent_buffer *eb)
wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
write_lock(&eb->lock);
- if (atomic_read(&eb->blocking_readers)) {
+ if (atomic_read(&eb->blocking_readers) ||
+ atomic_read(&eb->blocking_writers)) {
write_unlock(&eb->lock);
- wait_event(eb->read_lock_wq,
- atomic_read(&eb->blocking_readers) == 0);
- goto again;
- }
- if (atomic_read(&eb->blocking_writers)) {
- write_unlock(&eb->lock);
- wait_event(eb->write_lock_wq,
- atomic_read(&eb->blocking_writers) == 0);
goto again;
}
WARN_ON(atomic_read(&eb->spinning_writers));
Currently, the number of readers and writers is checked and in case there are any, wait and redo the locks. There's some duplication before the branches go back to again label, eg. calling wait_event on blocking_readers twice. The sequence is transformed loop: * wait for readers * wait for writers * write_lock * check readers, unlock and wait for readers, loop * check writers, unlock and wait for writers, loop The new sequence is not exactly the same due to the simplification, for readers it's slightly faster. For the writers, original code does * wait for writers * (loop) wait for readers * wait for writers -- again while the new goes directly to the reader check. This should behave the same on a contended lock with multiple writers and readers, but can reduce number of times we're waiting on something. Signed-off-by: David Sterba <dsterba@suse.com> --- fs/btrfs/locking.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-)