On Mon, Jul 01, 2019 at 08:47:29AM -0700, Bart Van Assche wrote:
> No code that occurs between blk_mq_get_ctx() and blk_mq_put_ctx() depends
> on preemption being disabled for its correctness. Since removing the CPU
> preemption calls does not measurably affect performance, simplify the
> blk-mq code by removing the blk_mq_put_ctx() function and also by not
> disabling preemption in blk_mq_get_ctx().
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-mq-sched.c | 5 +----
> block/blk-mq-tag.c | 8 --------
> block/blk-mq.c | 16 +++-------------
> block/blk-mq.h | 7 +------
> block/kyber-iosched.c | 1 -
> 5 files changed, 5 insertions(+), 32 deletions(-)
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 956a7aa9a637..c9d183d6c499 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -330,10 +330,8 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
> bool ret = false;
> enum hctx_type type;
>
> - if (e && e->type->ops.bio_merge) {
> - blk_mq_put_ctx(ctx);
> + if (e && e->type->ops.bio_merge)
> return e->type->ops.bio_merge(hctx, bio, nr_segs);
> - }
>
> type = hctx->type;
> if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
> @@ -344,7 +342,6 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
> spin_unlock(&ctx->lock);
> }
>
> - blk_mq_put_ctx(ctx);
> return ret;
> }
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 7513c8eaabee..da19f0bc8876 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -113,7 +113,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> struct sbq_wait_state *ws;
> DEFINE_SBQ_WAIT(wait);
> unsigned int tag_offset;
> - bool drop_ctx;
> int tag;
>
> if (data->flags & BLK_MQ_REQ_RESERVED) {
> @@ -136,7 +135,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> return BLK_MQ_TAG_FAIL;
>
> ws = bt_wait_ptr(bt, data->hctx);
> - drop_ctx = data->ctx == NULL;
> do {
> struct sbitmap_queue *bt_prev;
>
> @@ -161,9 +159,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> if (tag != -1)
> break;
>
> - if (data->ctx)
> - blk_mq_put_ctx(data->ctx);
> -
> bt_prev = bt;
> io_schedule();
>
> @@ -189,9 +184,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> ws = bt_wait_ptr(bt, data->hctx);
> } while (1);
>
> - if (drop_ctx && data->ctx)
> - blk_mq_put_ctx(data->ctx);
> -
> sbitmap_finish_wait(bt, ws, &wait);
>
> found_tag:
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2f0b14d2ecdc..4d661545ad1d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -359,13 +359,13 @@ static struct request *blk_mq_get_request(struct request_queue *q,
> struct elevator_queue *e = q->elevator;
> struct request *rq;
> unsigned int tag;
> - bool put_ctx_on_error = false;
> + bool clear_ctx_on_error = false;
>
> blk_queue_enter_live(q);
> data->q = q;
> if (likely(!data->ctx)) {
> data->ctx = blk_mq_get_ctx(q);
> - put_ctx_on_error = true;
> + clear_ctx_on_error = true;
> }
> if (likely(!data->hctx))
> data->hctx = blk_mq_map_queue(q, data->cmd_flags,
> @@ -391,10 +391,8 @@ static struct request *blk_mq_get_request(struct request_queue *q,
>
> tag = blk_mq_get_tag(data);
> if (tag == BLK_MQ_TAG_FAIL) {
> - if (put_ctx_on_error) {
> - blk_mq_put_ctx(data->ctx);
> + if (clear_ctx_on_error)
> data->ctx = NULL;
> - }
> blk_queue_exit(q);
> return NULL;
> }
> @@ -431,8 +429,6 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
> if (!rq)
> return ERR_PTR(-EWOULDBLOCK);
>
> - blk_mq_put_ctx(alloc_data.ctx);
> -
> rq->__data_len = 0;
> rq->__sector = (sector_t) -1;
> rq->bio = rq->biotail = NULL;
> @@ -1981,7 +1977,6 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
>
> plug = current->plug;
> if (unlikely(is_flush_fua)) {
> - blk_mq_put_ctx(data.ctx);
> blk_mq_bio_to_request(rq, bio, nr_segs);
>
> /* bypass scheduler for flush rq */
> @@ -1995,7 +1990,6 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
> unsigned int request_count = plug->rq_count;
> struct request *last = NULL;
>
> - blk_mq_put_ctx(data.ctx);
> blk_mq_bio_to_request(rq, bio, nr_segs);
>
> if (!request_count)
> @@ -2029,8 +2023,6 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
> blk_add_rq_to_plug(plug, rq);
> trace_block_plug(q);
>
> - blk_mq_put_ctx(data.ctx);
> -
> if (same_queue_rq) {
> data.hctx = same_queue_rq->mq_hctx;
> trace_block_unplug(q, 1, true);
> @@ -2039,11 +2031,9 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
> }
> } else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
> !data.hctx->dispatch_busy)) {
> - blk_mq_put_ctx(data.ctx);
> blk_mq_bio_to_request(rq, bio, nr_segs);
> blk_mq_try_issue_directly(data.hctx, rq, &cookie);
> } else {
> - blk_mq_put_ctx(data.ctx);
> blk_mq_bio_to_request(rq, bio, nr_segs);
> blk_mq_sched_insert_request(rq, false, true, true);
> }
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 633a5a77ee8b..f4bf5161333e 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -151,12 +151,7 @@ static inline struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q,
> */
> static inline struct blk_mq_ctx *blk_mq_get_ctx(struct request_queue *q)
> {
> - return __blk_mq_get_ctx(q, get_cpu());
> -}
> -
> -static inline void blk_mq_put_ctx(struct blk_mq_ctx *ctx)
> -{
> - put_cpu();
> + return __blk_mq_get_ctx(q, raw_smp_processor_id());
> }
Then there isn't any difference between __blk_mq_get_ctx() and blk_mq_get_ctx(),
so could you kill __blk_mq_get_ctx()?
Otherwise, looks fine:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
