On Tue, May 23, 2017 at 07:47:36PM +0800, Ming Lei wrote:
> Because what the per-sw-queue bio merge does is basically same with
> scheduler's .bio_merge(), this patch makes per-sw-queue bio merge
> as the default .bio_merge if no scheduler is used or io scheduler
> doesn't provide .bio_merge().
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq-sched.c | 62 +++++++++++++++++++++++++++++++++++++++++++++----
> block/blk-mq-sched.h | 4 +---
> block/blk-mq.c | 65 ----------------------------------------------------
> 3 files changed, 58 insertions(+), 73 deletions(-)
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 1f5b692526ae..c4e2afb9d12d 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -221,19 +221,71 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
> }
> EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
>
> +/*
> + * Reverse check our software queue for entries that we could potentially
> + * merge with. Currently includes a hand-wavy stop count of 8, to not spend
> + * too much time checking for merges.
> + */
> +static bool blk_mq_attempt_merge(struct request_queue *q,
> + struct blk_mq_ctx *ctx, struct bio *bio)
> +{
> + struct request *rq;
> + int checked = 8;
> +
> + list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
> + bool merged = false;
> +
> + if (!checked--)
> + break;
> +
> + if (!blk_rq_merge_ok(rq, bio))
> + continue;
> +
> + switch (blk_try_merge(rq, bio)) {
> + case ELEVATOR_BACK_MERGE:
> + if (blk_mq_sched_allow_merge(q, rq, bio))
> + merged = bio_attempt_back_merge(q, rq, bio);
> + break;
> + case ELEVATOR_FRONT_MERGE:
> + if (blk_mq_sched_allow_merge(q, rq, bio))
> + merged = bio_attempt_front_merge(q, rq, bio);
> + break;
> + case ELEVATOR_DISCARD_MERGE:
> + merged = bio_attempt_discard_merge(q, rq, bio);
> + break;
> + default:
> + continue;
> + }
> +
> + if (merged)
> + ctx->rq_merged++;
> + return merged;
> + }
> +
> + return false;
> +}
> +
> bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
> {
> struct elevator_queue *e = q->elevator;
> + struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
> + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
> + bool ret = false;
>
> + if (e && e->type->ops.mq.bio_merge) {
> blk_mq_put_ctx(ctx);
> return e->type->ops.mq.bio_merge(hctx, bio);
> }
>
> + if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) {
> + /* default per sw-queue merge */
> + spin_lock(&ctx->lock);
> + ret = blk_mq_attempt_merge(q, ctx, bio);
> + spin_unlock(&ctx->lock);
> + }
> +
> + blk_mq_put_ctx(ctx);
> + return ret;
I'd rather move __blk_mq_sched_bio_merge/blk_mq_sched_bio_merge into
blk-mq.c (and dropping the sched in the name) rather than moving
blk_mq_attempt_merge out.
But except that this looks fine to me.
