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dm table: set flush capability based on underlying devices

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DM has always advertised both REQ_FLUSH and REQ_FUA flush capabilities
regardless of whether or not a given DM device's underlying devices
also advertised a need for them.

Block's flush-merge changes from 2.6.39 have proven to be more costly
for DM devices.  Performance regressions have been reported even when
DM's underlying devices do not advertise that they have a write cache.

Fix the performance regressions by configuring a DM device's flushing
capabilities based on those of the underlying devices' capabilities.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2011-08-02 12:32:08 +01:00 committed by Alasdair G Kergon
parent 772ae5f54d
commit ed8b752bcc
2 changed files with 43 additions and 1 deletions
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43
drivers/md/dm-table.c
View File

@ -1248,9 +1248,45 @@ static void dm_table_set_integrity(struct dm_table *t)
blk_get_integrity(template_disk));
}
static int device_flush_capable(struct dm_target *ti, struct dm_dev *dev,
sector_t start, sector_t len, void *data)
{
unsigned flush = (*(unsigned *)data);
struct request_queue *q = bdev_get_queue(dev->bdev);
return q && (q->flush_flags & flush);
}
static bool dm_table_supports_flush(struct dm_table *t, unsigned flush)
{
struct dm_target *ti;
unsigned i = 0;
/*
* Require at least one underlying device to support flushes.
* t->devices includes internal dm devices such as mirror logs
* so we need to use iterate_devices here, which targets
* supporting flushes must provide.
*/
while (i < dm_table_get_num_targets(t)) {
ti = dm_table_get_target(t, i++);
if (!ti->num_flush_requests)
continue;
if (ti->type->iterate_devices &&
ti->type->iterate_devices(ti, device_flush_capable, &flush))
return 1;
}
return 0;
}
void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
struct queue_limits *limits)
{
unsigned flush = 0;
/*
* Copy table's limits to the DM device's request_queue
*/
@ -1261,6 +1297,13 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
else
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
if (dm_table_supports_flush(t, REQ_FLUSH)) {
flush |= REQ_FLUSH;
if (dm_table_supports_flush(t, REQ_FUA))
flush |= REQ_FUA;
}
blk_queue_flush(q, flush);
dm_table_set_integrity(t);
/*

1
drivers/md/dm.c
View File

@ -1808,7 +1808,6 @@ static void dm_init_md_queue(struct mapped_device *md)
blk_queue_make_request(md->queue, dm_request);
blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
blk_queue_merge_bvec(md->queue, dm_merge_bvec);
blk_queue_flush(md->queue, REQ_FLUSH | REQ_FUA);
}
/*