aboutsummaryrefslogtreecommitdiff
path: root/block
diff options
context:
space:
mode:
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 /block
parent30e0dc28bff9dc456cdfc2aae4aca78b8b1a1cec (diff)
downloadlinux-2.6.34-ux500-a6f23657d3072bde6844055bbc2290e497f33fbc.tar.gz
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 'block')
-rw-r--r--block/genhd.c23
1 files changed, 19 insertions, 4 deletions
diff --git a/block/genhd.c b/block/genhd.c
index 2f7feda61e3..d84a7df1e2a 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -181,6 +181,12 @@ void disk_part_iter_exit(struct disk_part_iter *piter)
}
EXPORT_SYMBOL_GPL(disk_part_iter_exit);
+static inline int sector_in_part(struct hd_struct *part, sector_t sector)
+{
+ return part->start_sect <= sector &&
+ sector < part->start_sect + part->nr_sects;
+}
+
/**
* disk_map_sector_rcu - map sector to partition
* @disk: gendisk of interest
@@ -199,16 +205,22 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit);
struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
{
struct disk_part_tbl *ptbl;
+ struct hd_struct *part;
int i;
ptbl = rcu_dereference(disk->part_tbl);
+ part = rcu_dereference(ptbl->last_lookup);
+ if (part && sector_in_part(part, sector))
+ return part;
+
for (i = 1; i < ptbl->len; i++) {
- struct hd_struct *part = rcu_dereference(ptbl->part[i]);
+ part = rcu_dereference(ptbl->part[i]);
- if (part && part->start_sect <= sector &&
- sector < part->start_sect + part->nr_sects)
+ if (part && sector_in_part(part, sector)) {
+ rcu_assign_pointer(ptbl->last_lookup, part);
return part;
+ }
}
return &disk->part0;
}
@@ -888,8 +900,11 @@ static void disk_replace_part_tbl(struct gendisk *disk,
struct disk_part_tbl *old_ptbl = disk->part_tbl;
rcu_assign_pointer(disk->part_tbl, new_ptbl);
- if (old_ptbl)
+
+ if (old_ptbl) {
+ rcu_assign_pointer(old_ptbl->last_lookup, NULL);
call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
+ }
}
/**