linux-kernel - Re: [PATCH v1 6/6] blk-mq: mark ctx as pending at batch in flush plug path

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Date:	Mon, 19 Oct 2015 11:57:10 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Ming Lin <ming.l@....samsung.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v1 6/6] blk-mq: mark ctx as pending at batch in flush plug path

Ming Lei <ming.lei@...onical.com> writes:

> Most of times, flush plug should be the hottest I/O path,
> so mark ctx as pending after all requests in the list are
> inserted.
>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>

I agree this looks like a better approach.  Whether it makes a
difference or not, I can't say.

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>

> ---
>  block/blk-mq.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a5e33bc..b169e2d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -990,18 +990,25 @@ void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
>  }
>  EXPORT_SYMBOL(blk_mq_delay_queue);
>  
> -static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
> -				    struct request *rq, bool at_head)
> +static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
> +					    struct blk_mq_ctx *ctx,
> +					    struct request *rq,
> +					    bool at_head)
>  {
> -	struct blk_mq_ctx *ctx = rq->mq_ctx;
> -
>  	trace_block_rq_insert(hctx->queue, rq);
>  
>  	if (at_head)
>  		list_add(&rq->queuelist, &ctx->rq_list);
>  	else
>  		list_add_tail(&rq->queuelist, &ctx->rq_list);
> +}
> +
> +static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
> +				    struct request *rq, bool at_head)
> +{
> +	struct blk_mq_ctx *ctx = rq->mq_ctx;
>  
> +	__blk_mq_insert_req_list(hctx, ctx, rq, at_head);
>  	blk_mq_hctx_mark_pending(hctx, ctx);
>  }
>  
> @@ -1057,8 +1064,9 @@ static void blk_mq_insert_requests(struct request_queue *q,
>  		rq = list_first_entry(list, struct request, queuelist);
>  		list_del_init(&rq->queuelist);
>  		rq->mq_ctx = ctx;
> -		__blk_mq_insert_request(hctx, rq, false);
> +		__blk_mq_insert_req_list(hctx, ctx, rq, false);
>  	}
> +	blk_mq_hctx_mark_pending(hctx, ctx);
>  	spin_unlock(&ctx->lock);
>  
>  	blk_mq_run_hw_queue(hctx, from_schedule);
--
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