From: Chengkaitao In the initial implementation, the 'list_add(&rq->queuelist, ...' statement added to the dd_insert_request function was designed to differentiate priorities among various IO-requests within the same linked list. For example, 'Commit 945ffb60c11d ("mq-deadline: add blk-mq adaptation of the deadline IO scheduler")', introduced this 'list_add' operation to ensure that requests with the at_head flag would always be dispatched before requests without the REQ_TYPE_FS flag. Since 'Commit 7687b38ae470 ("bfq/mq-deadline: remove redundant check for passthrough request")', removed blk_rq_is_passthrough, the dd->dispatch list now contains only requests with the at_head flag. In this context, all at_head requests should be treated as having equal priority, and a first-in-first-out (FIFO) policy better aligns with the current situation. Therefore, replacing list_add with list_add_tail is more appropriate. Signed-off-by: Chengkaitao --- block/mq-deadline.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/mq-deadline.c b/block/mq-deadline.c index 3e3719093aec..dcd7f4f1ecd2 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -661,7 +661,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, trace_block_rq_insert(rq); if (flags & BLK_MQ_INSERT_AT_HEAD) { - list_add(&rq->queuelist, &dd->dispatch); + list_add_tail(&rq->queuelist, &dd->dispatch); rq->fifo_time = jiffies; } else { deadline_add_rq_rb(per_prio, rq); -- 2.50.1 (Apple Git-155)