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yaml --- r: 110460 b: refs/heads/master c: 6a421c1 h: refs/heads/master v: v3
git-mirror · Oct 9, 2008 · e9cfce0 · e9cfce0
1 parent 31c84aa
commit e9cfce0
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Showing 2 changed files with 11 additions and 5 deletions.
diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4fb72f7646e86874eb2798256eaa6bf3fbe4edcf
+refs/heads/master: 6a421c1dc94b12923294a359822346f12492de5e
diff --git a/trunk/Documentation/block/deadline-iosched.txt b/trunk/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)