block: add one-hit cache for disk partition lookup

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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>

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This commit is contained in:

Jens Axboe 2008-10-24 12:52:42 +02:00

parent 30e0dc28bf

commit a6f23657d3

2 changed files with 20 additions and 4 deletions

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include/linux/genhd.h

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