From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: [PATCH] dm: do not call dm_sync_table() when creating new devices Date: Wed, 5 Nov 2014 14:35:50 +0100 Message-ID: <1415194550-121498-1-git-send-email-hare@suse.de> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer Cc: dm-devel@redhat.com, Alasdair Kergon List-Id: dm-devel.ids When creating new devices dm_sync_table() calls synchronize_rcu_expedited(), causing _all_ pending RCU pointers to be flushed. This causes a latency overhead especially noticeable when creating lots of devices. And all of this is pointless as there are no old maps to be disconnected, and hence no stale pointers which would need to be cleared up. Signed-off-by: Hannes Reinecke --- drivers/md/dm.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 58f3927..2c2c6cf 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2341,7 +2341,8 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t, set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags); else clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags); - dm_sync_table(md); + if (old_map) + dm_sync_table(md); return old_map; } @@ -2782,7 +2783,8 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) * flush_workqueue(md->wq). */ set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags); - synchronize_srcu(&md->io_barrier); + if (map) + synchronize_srcu(&md->io_barrier); /* * Stop md->queue before flushing md->wq in case request-based @@ -2802,7 +2804,8 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) if (noflush) clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags); - synchronize_srcu(&md->io_barrier); + if (map) + synchronize_srcu(&md->io_barrier); /* were we interrupted ? */ if (r < 0) { -- 1.8.5.2