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author | Aaron Carroll <aaronc@gelato.unsw.edu.au> | 2008-08-14 18:17:15 +1000 |
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committer | Jens Axboe <jens.axboe@oracle.com> | 2008-10-09 08:56:03 +0200 |
commit | 6a421c1dc94b12923294a359822346f12492de5e (patch) | |
tree | 4fcc60ba25a8ca9abc8607afae4a0eec46d38240 /Documentation | |
parent | 4fb72f7646e86874eb2798256eaa6bf3fbe4edcf (diff) | |
download | linux-stable-6a421c1dc94b12923294a359822346f12492de5e.tar.gz linux-stable-6a421c1dc94b12923294a359822346f12492de5e.tar.bz2 linux-stable-6a421c1dc94b12923294a359822346f12492de5e.zip |
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.txt | 14 |
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) Similar to read_expire mentioned above, but for writes. -fifo_batch +fifo_batch (number of requests) ---------- -When a read request expires its deadline, we must move some requests from -the sorted io scheduler list to the block device dispatch queue. fifo_batch -controls how many requests we move. +Requests are grouped into ``batches'' of a particular data direction (read or +write) which are serviced in increasing sector order. To limit extra seeking, +deadline expiries are only checked between batches. fifo_batch controls the +maximum number of requests per batch. + +This parameter tunes the balance between per-request latency and aggregate +throughput. When low latency is the primary concern, smaller is better (where +a value of 1 yields first-come first-served behaviour). Increasing fifo_batch +generally improves throughput, at the cost of latency variation. writes_starved (number of dispatches) |