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rbd: use binary search for snapshot lookup 

Use bsearch(3) to make snapshot lookup by id more efficient.  (There
could be thousands of snapshots, and conceivably many more.)

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
This commit is contained in:
Alex Elder 2013-05-01 12:43:03 -05:00
parent 15228ede7d
commit 30d1cff817
1 changed files with 29 additions and 5 deletions
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34
drivers/block/rbd.c
View File

@ -33,6 +33,7 @@
#include <linux/ceph/mon_client.h>
#include <linux/ceph/decode.h>
#include <linux/parser.h>
#include <linux/bsearch.h>
#include <linux/kernel.h>
#include <linux/device.h>
@ -819,16 +820,39 @@ static const char *_rbd_dev_v1_snap_name(struct rbd_device *rbd_dev, u32 which)
return kstrdup(snap_name, GFP_KERNEL);
}
/*
* Snapshot id comparison function for use with qsort()/bsearch().
* Note that result is for snapshots in *descending* order.
*/
static int snapid_compare_reverse(const void *s1, const void *s2)
{
u64 snap_id1 = *(u64 *)s1;
u64 snap_id2 = *(u64 *)s2;
if (snap_id1 < snap_id2)
return 1;
return snap_id1 == snap_id2 ? 0 : -1;
}
/*
* Search a snapshot context to see if the given snapshot id is
* present.
*
* Returns the position of the snapshot id in the array if it's found,
* or BAD_SNAP_INDEX otherwise.
*
* Note: The snapshot array is in kept sorted (by the osd) in
* reverse order, highest snapshot id first.
*/
static u32 rbd_dev_snap_index(struct rbd_device *rbd_dev, u64 snap_id)
{
struct ceph_snap_context *snapc = rbd_dev->header.snapc;
u32 which;
u64 *found;
for (which = 0; which < snapc->num_snaps; which++)
if (snapc->snaps[which] == snap_id)
return which;
found = bsearch(&snap_id, &snapc->snaps, snapc->num_snaps,
sizeof (snap_id), snapid_compare_reverse);
return BAD_SNAP_INDEX;
return found ? (u32)(found - &snapc->snaps[0]) : BAD_SNAP_INDEX;
}
static const char *rbd_dev_v1_snap_name(struct rbd_device *rbd_dev,