dm mpath: micro-optimize the hot path relative to MPATHF_QUEUE_IF_NO_PATH

Instead of checking MPATHF_QUEUE_IF_NO_PATH,
MPATHF_SAVED_QUEUE_IF_NO_PATH and the no_flush flag to decide whether
or not to push back a request (or bio) if there are no paths available,
only clear MPATHF_QUEUE_IF_NO_PATH in queue_if_no_path() if no_flush has
not been set.  The result is that only a single bit has to be tested in
the hot path to decide whether or not a request must be pushed back and
also that m->lock does not have to be taken in the hot path.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 11 insertions, 59 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 8336332bd61f..5cb1beccd1e2 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -442,47 +442,6 @@ failed:
 }
 
 /*
- * Check whether bios must be queued in the device-mapper core rather
- * than here in the target.
- *
- * If m->queue_if_no_path and m->saved_queue_if_no_path hold the
- * same value then we are not between multipath_presuspend()
- * and multipath_resume() calls and we have no need to check
- * for the DMF_NOFLUSH_SUSPENDING flag.
- */
-static bool __must_push_back(struct multipath *m)
-{
-        return ((test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) !=
-                 test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags)) &&
-                dm_noflush_suspending(m->ti));
-}
-
-static bool must_push_back_rq(struct multipath *m)
-{
-        bool r;
-        unsigned long flags;
-
-        spin_lock_irqsave(&m->lock, flags);
-        r = (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) ||
-             __must_push_back(m));
-        spin_unlock_irqrestore(&m->lock, flags);
-
-        return r;
-}
-
-static bool must_push_back_bio(struct multipath *m)
-{
-        bool r;
-        unsigned long flags;
-
-        spin_lock_irqsave(&m->lock, flags);
-        r = __must_push_back(m);
-        spin_unlock_irqrestore(&m->lock, flags);
-
-        return r;
-}
-
-/*
  * Map cloned requests (request-based multipath)
  */
 static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
@@ -503,7 +462,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
                 pgpath = choose_pgpath(m, nr_bytes);
 
         if (!pgpath) {
-                if (must_push_back_rq(m))
+                if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
                         return DM_MAPIO_DELAY_REQUEUE;
                 return -EIO;    /* Failed */
         } else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||
@@ -580,9 +539,9 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
         }
 
         if (!pgpath) {
-                if (!must_push_back_bio(m))
-                        return -EIO;
-                return DM_MAPIO_REQUEUE;
+                if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+                        return DM_MAPIO_REQUEUE;
+                return -EIO;
         }
 
         mpio->pgpath = pgpath;
@@ -674,7 +633,7 @@ static int queue_if_no_path(struct multipath *m, bool queue_if_no_path,
                 else
                         clear_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags);
         }
-        if (queue_if_no_path)
+        if (queue_if_no_path || dm_noflush_suspending(m->ti))
                 set_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);
         else
                 clear_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);
@@ -1519,12 +1478,9 @@ static int do_end_io(struct multipath *m, struct request *clone,
         if (mpio->pgpath)
                 fail_path(mpio->pgpath);
 
-        if (!atomic_read(&m->nr_valid_paths)) {
-                if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
-                        if (!must_push_back_rq(m))
-                                r = -EIO;
-                }
-        }
+        if (atomic_read(&m->nr_valid_paths) == 0 &&
+            !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+                r = -EIO;
 
         return r;
 }
@@ -1565,13 +1521,9 @@ static int do_end_io_bio(struct multipath *m, struct bio *clone,
         if (mpio->pgpath)
                 fail_path(mpio->pgpath);
 
-        if (!atomic_read(&m->nr_valid_paths)) {
-                if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
-                        if (!must_push_back_bio(m))
-                                return -EIO;
-                        return DM_ENDIO_REQUEUE;
-                }
-        }
+        if (atomic_read(&m->nr_valid_paths) == 0 &&
+            !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+                return -EIO;
 
         /* Queue for the daemon to resubmit */
         dm_bio_restore(get_bio_details_from_bio(clone), clone);