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block: Remove unnecessary elevator operation checks

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The insert_requests and dispatch_request elevator operations are
mandatory for the correct execution of an elevator, and all implemented
elevators (bfq, kyber and mq-deadline) implement them. As a result,
there is no need to check for these operations before calling them when
a queue has an elevator set. This simplifies the code in
__blk_mq_sched_dispatch_requests() and blk_mq_sched_insert_request().

To avoid out-of-tree elevators to crash the kernel in case of bad
implementation, add a check in elv_register() to verify that these
operations are implemented.

A small, probably not significant, IOPS improvement of 0.1% is observed
with this patch applied (4.117 MIOPS to 4.123 MIOPS, average of 20 fio
runs doing 4K random direct reads with psync and 32 jobs).

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210618015922.713999-1-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Damien Le Moal 2021-06-18 10:59:22 +09:00 committed by Jens Axboe
parent f0c1c4d286
commit e42cfb1da0
2 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
block/blk-mq-sched.c
View File

@ -294,8 +294,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
const bool has_sched = q->elevator;
int ret = 0;
LIST_HEAD(rq_list);
@ -326,12 +325,12 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
if (!list_empty(&rq_list)) {
blk_mq_sched_mark_restart_hctx(hctx);
if (blk_mq_dispatch_rq_list(hctx, &rq_list, 0)) {
if (has_sched_dispatch)
if (has_sched)
ret = blk_mq_do_dispatch_sched(hctx);
else
ret = blk_mq_do_dispatch_ctx(hctx);
}
} else if (has_sched_dispatch) {
} else if (has_sched) {
ret = blk_mq_do_dispatch_sched(hctx);
} else if (hctx->dispatch_busy) {
/* dequeue request one by one from sw queue if queue is busy */
@ -463,7 +462,7 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
goto run;
}
if (e && e->type->ops.insert_requests) {
if (e) {
LIST_HEAD(list);
list_add(&rq->queuelist, &list);
@ -494,9 +493,9 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
percpu_ref_get(&q->q_usage_counter);
e = hctx->queue->elevator;
if (e && e->type->ops.insert_requests)
if (e) {
e->type->ops.insert_requests(hctx, list, false);
else {
} else {
/*
* try to issue requests directly if the hw queue isn't
* busy in case of 'none' scheduler, and this way may save

4
block/elevator.c
View File

@ -522,6 +522,10 @@ void elv_unregister_queue(struct request_queue *q)
int elv_register(struct elevator_type *e)
{
/* insert_requests and dispatch_request are mandatory */
if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))
return -EINVAL;
/* create icq_cache if requested */
if (e->icq_size) {
if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||