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block: Simplify blk_mq_dispatch_rq_list() and its callers 

The 'nr_budgets' argument of blk_mq_dispatch_rq_list() is either the
number of elements in the 'list' argument or zero. Instead of passing
the number of list elements to blk_mq_dispatch_rq_list(), pass a boolean
argument that indicates whether or not blk_mq_dispatch_rq_list() should
request the block driver for a budget for each request in 'list'.

Remove the code for counting list elements from blk_mq_dispatch_rq_list()
callers where possible. Remove the code that decrements nr_budgets from
blk_mq_dispatch_rq_list() because it is superfluous. Each request that
is processed by blk_mq_dispatch_rq_list() is in one of these two states
if 'get_budget' is false:
* Either the request is on 'list' and the budget for the request has to
  be released from the error path.
* Or the request is not on 'list' and q->mq_ops->queue_rq() has already
  released the budget (ret != BLK_STS_OK) or q->mq_ops->queue_rq() will
  release the budget asynchronously (ret == BLK_STS_OK).

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20250415205134.3650042-1-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2025-04-15 13:51:34 -07:00 committed by Jens Axboe
parent 9d7a0577c9
commit e093b784ab
3 changed files with 13 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
block/blk-mq-sched.c
View File

@ -59,19 +59,17 @@ static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
struct request *rq;
LIST_HEAD(hctx_list);
unsigned int count = 0;
list_for_each_entry(rq, rq_list, queuelist) {
if (rq->mq_hctx != hctx) {
list_cut_before(&hctx_list, rq_list, &rq->queuelist);
goto dispatch;
}
count++;
}
list_splice_tail_init(rq_list, &hctx_list);
dispatch:
return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
return blk_mq_dispatch_rq_list(hctx, &hctx_list, false);
}
#define BLK_MQ_BUDGET_DELAY 3 /* ms units */
@ -167,7 +165,7 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
} while (!list_empty(&rq_list));
} else {
dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, false);
}
if (busy)
@ -261,7 +259,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
/* round robin for fair dispatch */
ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, false));
WRITE_ONCE(hctx->dispatch_from, ctx);
return ret;
@ -298,7 +296,7 @@ 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 (!blk_mq_dispatch_rq_list(hctx, &rq_list, true))
return 0;
need_dispatch = true;
} else {
@ -312,7 +310,7 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
if (need_dispatch)
return blk_mq_do_dispatch_ctx(hctx);
blk_mq_flush_busy_ctxs(hctx, &rq_list);
blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
blk_mq_dispatch_rq_list(hctx, &rq_list, true);
return 0;
}

16
block/blk-mq.c
View File

@ -2080,7 +2080,7 @@ static void blk_mq_commit_rqs(struct blk_mq_hw_ctx *hctx, int queued,
* Returns true if we did some work AND can potentially do more.
*/
bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
unsigned int nr_budgets)
bool get_budget)
{
enum prep_dispatch prep;
struct request_queue *q = hctx->queue;
@ -2102,7 +2102,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
rq = list_first_entry(list, struct request, queuelist);
WARN_ON_ONCE(hctx != rq->mq_hctx);
prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);
prep = blk_mq_prep_dispatch_rq(rq, get_budget);
if (prep != PREP_DISPATCH_OK)
break;
@ -2111,12 +2111,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
bd.rq = rq;
bd.last = list_empty(list);
/*
* once the request is queued to lld, no need to cover the
* budget any more
*/
if (nr_budgets)
nr_budgets--;
ret = q->mq_ops->queue_rq(hctx, &bd);
switch (ret) {
case BLK_STS_OK:
@ -2150,7 +2144,11 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) ||
blk_mq_is_shared_tags(hctx->flags));
if (nr_budgets)
/*
* If the caller allocated budgets, free the budgets of the
* requests that have not yet been passed to the block driver.
*/
if (!get_budget)
blk_mq_release_budgets(q, list);
spin_lock(&hctx->lock);

2
block/blk-mq.h
View File

@ -48,7 +48,7 @@ void blk_mq_exit_queue(struct request_queue *q);
int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
void blk_mq_wake_waiters(struct request_queue *q);
bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *,
unsigned int);
bool);
void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);
struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *start);