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authorAaron Carroll <aaronc@gelato.unsw.edu.au>2007-10-30 10:40:13 +0100
committerJens Axboe <axboe@carl.home.kernel.dk>2007-11-02 08:47:25 +0100
commit6f5d8aa6382eef2b26032c88656270bdae7f0c42 (patch)
tree6ee855ce6e8b0eb8cb04d41579ac11cb25a92759
parentdfb3d72a9aa519672c9ae06f0d2f93eccb35482f (diff)
Deadline iosched: Fix batching fairness
After switching data directions, deadline always starts the next batch from the lowest-sector request. This gives excessive deadline expiries and large latency and throughput disparity between high- and low-sector requests; an order of magnitude in some tests. This patch changes the batching behaviour so new batches start from the request whose expiry is earliest. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--block/deadline-iosched.c21
1 files changed, 7 insertions, 14 deletions
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index cb94c838087..a054eef8dff 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -306,27 +306,20 @@ dispatch_writes:
dispatch_find_request:
/*
* we are not running a batch, find best request for selected data_dir
- * and start a new batch
*/
- if (deadline_check_fifo(dd, data_dir)) {
- /* An expired request exists - satisfy it */
+ if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
+ /*
+ * A deadline has expired, the last request was in the other
+ * direction, or we have run out of higher-sectored requests.
+ * Start again from the request with the earliest expiry time.
+ */
rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
- } else if (dd->next_rq[data_dir]) {
+ } else {
/*
* The last req was the same dir and we have a next request in
* sort order. No expired requests so continue on from here.
*/
rq = dd->next_rq[data_dir];
- } else {
- struct rb_node *node;
- /*
- * The last req was the other direction or we have run out of
- * higher-sectored requests. Go back to the lowest sectored
- * request (1 way elevator) and start a new batch.
- */
- node = rb_first(&dd->sort_list[data_dir]);
- if (node)
- rq = rb_entry_rq(node);
}
dd->batching = 0;