Commit 6f5d8aa6 authored by Aaron Carroll's avatar Aaron Carroll Committed by Jens Axboe

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: default avatarAaron Carroll <>
Signed-off-by: default avatarJens Axboe <>
parent dfb3d72a
......@@ -306,27 +306,20 @@ static int deadline_dispatch_requests(struct request_queue *q, int force)
* 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;
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