On 2020/06/02 18:15, Ming Lei wrote:
> Move code for getting driver tag and budget into one helper, so
> blk_mq_dispatch_rq_list gets a bit simplified, and easier to read.
>
> Meantime move updating of 'no_tag' and 'no_budget_available' into
> the branch for handling partial dispatch because that is exactly
> consumer of the two local variables.
>
> Also rename the parameter of 'got_budget' as 'ask_budget'.
>
> No functional change.
>
> Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Cc: Baolin Wang <baolin.wang7@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Reviewed-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> Tested-by: Baolin Wang <baolin.wang7@xxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq.c | 75 +++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 49 insertions(+), 26 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 723bc39507fe..ee9342aac7be 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1233,18 +1233,51 @@ static void blk_mq_handle_zone_resource(struct request *rq,
> __blk_mq_requeue_request(rq);
> }
>
> +enum prep_dispatch {
> + PREP_DISPATCH_OK,
> + PREP_DISPATCH_NO_TAG,
> + PREP_DISPATCH_NO_BUDGET,
> +};
> +
> +static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
> + bool ask_budget)
"need_budget" may be a better argument name instead of ask_budget. More
reflective of the fact that this is a boolean.
> +{
> + struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
> +
> + if (ask_budget && !blk_mq_get_dispatch_budget(rq->q)) {
> + blk_mq_put_driver_tag(rq);
> + return PREP_DISPATCH_NO_BUDGET;
> + }
> +
> + if (!blk_mq_get_driver_tag(rq)) {
> + /*
> + * The initial allocation attempt failed, so we need to
> + * rerun the hardware queue when a tag is freed. The
> + * waitqueue takes care of that. If the queue is run
> + * before we add this entry back on the dispatch list,
> + * we'll re-run it below.
> + */
> + if (!blk_mq_mark_tag_wait(hctx, rq)) {
> + /* budget is always obtained before getting tag */
This is clear since it was down a few lines above. Maybe drop this comment ?
> + blk_mq_put_dispatch_budget(rq->q);
> + return PREP_DISPATCH_NO_TAG;
> + }
> + }
> +
> + return PREP_DISPATCH_OK;
> +}
> +
> /*
> * 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,
> bool got_budget)
> {
> + enum prep_dispatch prep;
> struct request_queue *q = hctx->queue;
> struct request *rq, *nxt;
> - bool no_tag = false;
> int errors, queued;
> blk_status_t ret = BLK_STS_OK;
> - bool no_budget_avail = false;
> LIST_HEAD(zone_list);
>
> if (list_empty(list))
> @@ -1262,31 +1295,9 @@ 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);
> - if (!got_budget && !blk_mq_get_dispatch_budget(q)) {
> - blk_mq_put_driver_tag(rq);
> - no_budget_avail = true;
> + prep = blk_mq_prep_dispatch_rq(rq, !got_budget);
> + if (prep != PREP_DISPATCH_OK)
> break;
> - }
> -
> - if (!blk_mq_get_driver_tag(rq)) {
> - /*
> - * The initial allocation attempt failed, so we need to
> - * rerun the hardware queue when a tag is freed. The
> - * waitqueue takes care of that. If the queue is run
> - * before we add this entry back on the dispatch list,
> - * we'll re-run it below.
> - */
> - if (!blk_mq_mark_tag_wait(hctx, rq)) {
> - blk_mq_put_dispatch_budget(q);
> - /*
> - * For non-shared tags, the RESTART check
> - * will suffice.
> - */
> - if (hctx->flags & BLK_MQ_F_TAG_SHARED)
> - no_tag = true;
> - break;
> - }
> - }
>
> list_del_init(&rq->queuelist);
>
> @@ -1339,6 +1350,18 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
> */
> if (!list_empty(list)) {
> bool needs_restart;
> + bool no_tag = false;
> + bool no_budget_avail = false;
> +
> + /*
> + * For non-shared tags, the RESTART check
> + * will suffice.
> + */
> + if (prep == PREP_DISPATCH_NO_TAG &&
> + (hctx->flags & BLK_MQ_F_TAG_SHARED))
> + no_tag = true;
You could drop the variable declaration initialization and simply have:
no_tag = prep == PREP_DISPATCH_NO_TAG &&
(hctx->flags & BLK_MQ_F_TAG_SHARED)
> + if (prep == PREP_DISPATCH_NO_BUDGET)
> + no_budget_avail = true;
Same here:
no_budget = prep == PREP_DISPATCH_NO_BUDGET;
Also to be symmetric with "no_tag", "no_budget" may be a better variable name ?
>
> /*
> * If we didn't flush the entire list, we could have told
>
--
Damien Le Moal
Western Digital Research
