From 30d1cff817808fca9801c743d2de4c61f3f38e15 Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Wed, 1 May 2013 12:43:03 -0500 Subject: [PATCH] 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 Reviewed-by: Josh Durgin --- drivers/block/rbd.c | 34 +++++++++++++++++++++++++++++----- 1 file changed, 29 insertions(+), 5 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 3f58aba6461f..82d9586a4172 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -33,6 +33,7 @@ #include #include #include +#include #include #include @@ -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, -- 2.20.1