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SubjectRe: [PATCH V7 1/4] blk-mq: refactor the code of issue request directly
On Wed, Nov 14, 2018 at 04:45:28PM +0800, Jianchao Wang wrote:
> Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
> into one interface to unify the interfaces to issue requests
> directly. The merged interface takes over the requests totally,
> it could insert, end or do nothing based on the return value of
> .queue_rq and 'bypass' parameter. Then caller needn't any other
> handling any more.
>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
> ---
> block/blk-mq.c | 93 ++++++++++++++++++++++++++++------------------------------
> 1 file changed, 45 insertions(+), 48 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 411be60..14b4d06 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1766,78 +1766,75 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
> return ret;
> }
>
> -static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> +static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> struct request *rq,
> blk_qc_t *cookie,
> - bool bypass_insert)
> + bool bypass)
> {
> struct request_queue *q = rq->q;
> bool run_queue = true;
> + blk_status_t ret = BLK_STS_RESOURCE;
> + int srcu_idx;
>
> + hctx_lock(hctx, &srcu_idx);
> /*
> - * RCU or SRCU read lock is needed before checking quiesced flag.
> + * hctx_lock is needed before checking quiesced flag.
> *
> - * When queue is stopped or quiesced, ignore 'bypass_insert' from
> - * blk_mq_request_issue_directly(), and return BLK_STS_OK to caller,
> - * and avoid driver to try to dispatch again.
> + * When queue is stopped or quiesced, ignore 'bypass', insert
> + * and return BLK_STS_OK to caller, and avoid driver to try to
> + * dispatch again.
> */
> - if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
> + if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) {
> run_queue = false;
> - bypass_insert = false;
> - goto insert;
> + bypass = false;
> + goto out_unlock;
> }
>
> - if (q->elevator && !bypass_insert)
> - goto insert;
> + /*
> + * Bypass the potential scheduler on the bottom device.
> + */
> + if (unlikely(q->elevator && !bypass))
> + goto out_unlock;
>
> - if (!blk_mq_get_dispatch_budget(hctx))
> - goto insert;
> + if (unlikely(!blk_mq_get_dispatch_budget(hctx)))
> + goto out_unlock;

The unlikely annotation is a bit misleading, since out-of-budget can
happen frequently in case of low queue depth, and there are lots of
such examples.

>
> - if (!blk_mq_get_driver_tag(rq)) {
> + if (unlikely(!blk_mq_get_driver_tag(rq))) {

Same with above.

Thanks,
Ming

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