From 6f5d8aa6382eef2b26032c88656270bdae7f0c42 Mon Sep 17 00:00:00 2001 From: Aaron Carroll Date: Tue, 30 Oct 2007 10:40:13 +0100 Subject: [PATCH] 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 Signed-off-by: Jens Axboe --- block/deadline-iosched.c | 21 +++++++-------------- 1 file 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; -- 2.41.1