From: Martin Wilck mwilck@suse.com
[ Upstream commit 2361ae595352dec015d14292f1b539242d8446d6 ]
SCSI LUN passthrough code such as qemu's "scsi-block" device model pass every IO to the host via SG_IO ioctls. Currently, dm-multipath calls choose_pgpath() only in the block IO code path, not in the ioctl code path (unless current_pgpath is NULL). This has the effect that no path switching and thus no load balancing is done for SCSI-passthrough IO, unless the active path fails.
Fix this by using the same logic in multipath_prepare_ioctl() as in multipath_clone_and_map().
Note: The allegedly best path selection algorithm, service-time, still wouldn't work perfectly, because the io size of the current request is always set to 0. Changing that for the IO passthrough case would require the ioctl cmd and arg to be passed to dm's prepare_ioctl() method.
Signed-off-by: Martin Wilck mwilck@suse.com Reviewed-by: Hannes Reinecke hare@suse.de Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm-mpath.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c index 456d790c918c..f2de4c73cc8f 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -1856,7 +1856,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti, int r;
current_pgpath = READ_ONCE(m->current_pgpath); - if (!current_pgpath) + if (!current_pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags)) current_pgpath = choose_pgpath(m, 0);
if (current_pgpath) {