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authorAaron Carroll <aaronc@gelato.unsw.edu.au>2008-08-14 04:17:15 -0400
committerJens Axboe <jens.axboe@oracle.com>2008-10-09 02:56:03 -0400
commit6a421c1dc94b12923294a359822346f12492de5e (patch)
tree4fcc60ba25a8ca9abc8607afae4a0eec46d38240 /Documentation
parent4fb72f7646e86874eb2798256eaa6bf3fbe4edcf (diff)
block: update documentation for deadline fifo_batch tunable
Update the description of fifo_batch to match the current implementation, and include a description of how to tune it. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/block/deadline-iosched.txt14
1 files changed, 10 insertions, 4 deletions
diff --git a/Documentation/block/deadline-iosched.txt b/Documentation/block/deadline-iosched.txt
index c23cab13c3d1..72576769e0f4 100644
--- a/Documentation/block/deadline-iosched.txt
+++ b/Documentation/block/deadline-iosched.txt
@@ -30,12 +30,18 @@ write_expire (in ms)
30Similar to read_expire mentioned above, but for writes. 30Similar to read_expire mentioned above, but for writes.
31 31
32 32
33fifo_batch 33fifo_batch (number of requests)
34---------- 34----------
35 35
36When a read request expires its deadline, we must move some requests from 36Requests are grouped into ``batches'' of a particular data direction (read or
37the sorted io scheduler list to the block device dispatch queue. fifo_batch 37write) which are serviced in increasing sector order. To limit extra seeking,
38controls how many requests we move. 38deadline expiries are only checked between batches. fifo_batch controls the
39maximum number of requests per batch.
40
41This parameter tunes the balance between per-request latency and aggregate
42throughput. When low latency is the primary concern, smaller is better (where
43a value of 1 yields first-come first-served behaviour). Increasing fifo_batch
44generally improves throughput, at the cost of latency variation.
39 45
40 46
41writes_starved (number of dispatches) 47writes_starved (number of dispatches)