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authorJens Axboe <jens.axboe@oracle.com>2008-10-24 12:52:42 +0200
committerJens Axboe <jens.axboe@oracle.com>2008-12-29 08:29:51 +0100
commita6f23657d3072bde6844055bbc2290e497f33fbc (patch)
treebd96916615d04228cc9492ae198ed5012d5ee86a /include/linux/genhd.h
parent30e0dc28bff9dc456cdfc2aae4aca78b8b1a1cec (diff)
block: add one-hit cache for disk partition lookup
disk_map_sector_rcu() returns a partition from a sector offset, which we use for IO statistics on a per-partition basis. The lookup itself is an O(N) list lookup, where N is the number of partitions. This actually hurts performance quite a bit, even on the lower end partitions. On higher numbered partitions, it can get pretty bad. Solve this by adding a one-hit cache for partition lookup. This makes the lookup O(1) for the case where we do most IO to one partition. Even for mixed partition workloads, amortized cost is pretty close to O(1) since the natural IO batching makes the one-hit cache last for lots of IOs. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'include/linux/genhd.h')
-rw-r--r--include/linux/genhd.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 3df7742ce246..16948eaecae3 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -126,6 +126,7 @@ struct blk_scsi_cmd_filter {
struct disk_part_tbl {
struct rcu_head rcu_head;
int len;
+ struct hd_struct *last_lookup;
struct hd_struct *part[];
};