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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>
This commit is contained in:
Bart Van Assche 2017-04-27 10:11:24 -07:00 committed by Mike Snitzer
parent 7e0d574f26
commit ca5beb76c3
1 changed files with 11 additions and 59 deletions
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70
drivers/md/dm-mpath.c
View File

@ -441,47 +441,6 @@ failed:
return NULL;
}
/*
* 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)
*/
@ -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);