-
Mike Snitzer authored
The primary motivation of this commit is to improve the scalability of DM multipath on large NUMA systems where m->lock spinlock contention has been proven to be a serious bottleneck on really fast storage. The ability to atomically read a pointer, using lockless_dereference(), is leveraged in this commit. But all pointer writes are still protected by the m->lock spinlock (which is fine since these all now occur in the slow-path). The following functions no longer require the m->lock spinlock in their fast-path: multipath_busy(), __multipath_map(), and do_end_io() And choose_pgpath() is modified to _not_ update m->current_pgpath unless it also switches the path-group. This is done to avoid needing to take the m->lock everytime __multipath_map() calls choose_pgpath(). But m->current_pgpath will be reset if it is failed via fail_path(). Suggested-by:
Jeff Moyer <jmoyer@redhat.com> Reviewed-by:
Hannes Reinecke <hare@suse.com> Tested-by:
Hannes Reinecke <hare@suse.com> Signed-off-by:
Mike Snitzer <snitzer@redhat.com>
2da1610a