* [PATCH] dm: do not call dm_sync_table() when creating new devices
@ 2014-11-05 13:35 Hannes Reinecke
2014-11-05 14:15 ` Mike Snitzer
2014-11-05 22:16 ` [PATCH] " Mikulas Patocka
0 siblings, 2 replies; 3+ messages in thread
From: Hannes Reinecke @ 2014-11-05 13:35 UTC (permalink / raw)
To: Mike Snitzer; +Cc: dm-devel, Alasdair Kergon
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 <hare@suse.de>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: dm: do not call dm_sync_table() when creating new devices
2014-11-05 13:35 [PATCH] dm: do not call dm_sync_table() when creating new devices Hannes Reinecke
@ 2014-11-05 14:15 ` Mike Snitzer
2014-11-05 22:16 ` [PATCH] " Mikulas Patocka
1 sibling, 0 replies; 3+ messages in thread
From: Mike Snitzer @ 2014-11-05 14:15 UTC (permalink / raw)
To: Hannes Reinecke; +Cc: dm-devel, Alasdair Kergon
On Wed, Nov 05 2014 at 8:35am -0500,
Hannes Reinecke <hare@suse.de> wrote:
> 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 <hare@suse.de>
Looks good, I'll get it staged for 3.19 (will need to be rebased on the
linux-dm.git 'dm-for-3.19' branch given the suspend related refactoring
there, but I'll take care of it as needed).
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] dm: do not call dm_sync_table() when creating new devices
2014-11-05 13:35 [PATCH] dm: do not call dm_sync_table() when creating new devices Hannes Reinecke
2014-11-05 14:15 ` Mike Snitzer
@ 2014-11-05 22:16 ` Mikulas Patocka
1 sibling, 0 replies; 3+ messages in thread
From: Mikulas Patocka @ 2014-11-05 22:16 UTC (permalink / raw)
To: Hannes Reinecke; +Cc: dm-devel, Alasdair Kergon, Mike Snitzer
On Wed, 5 Nov 2014, Hannes Reinecke wrote:
> 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 <hare@suse.de>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
> ---
> 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
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-11-05 13:35 [PATCH] dm: do not call dm_sync_table() when creating new devices Hannes Reinecke
2014-11-05 14:15 ` Mike Snitzer
2014-11-05 22:16 ` [PATCH] " Mikulas Patocka
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