linux-kernel - Re: [RFC PATCH 1/7] blk-mq: Export blk_mq_hctx_has

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Date:   Mon, 22 Jul 2019 22:19:41 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     axboe@...nel.dk, adrian.hunter@...el.com, ulf.hansson@...aro.org,
        zhang.lyra@...il.com, orsonzhai@...il.com, arnd@...db.de,
        linus.walleij@...aro.org, vincent.guittot@...aro.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org
Subject: Re: [RFC PATCH 1/7] blk-mq: Export blk_mq_hctx_has_pending() function

On Mon, Jul 22, 2019 at 09:09:36PM +0800, Baolin Wang wrote:
> Some SD/MMC host controllers can support packed command or packed request,
> that means we can package several requests to host controller at one time
> to improve performence. And this patch set will introduce MMC packed function
> to support this feature by following patches.
> 
> To support MMC packed function, the MMC layer need to know if there are
> requests are pending now in hardware queue to help to combine requests
> as much as possible. If we know there are requests pending in hardware
> queue, then we should not package requests to host controller immediately,
> instead we should collect more requests into MMC packed queue to be packed
> to host controller with packed condition.
> 
> Thus export this function for MMC packed function.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> ---
>  block/blk-mq.c         |    3 ++-
>  include/linux/blk-mq.h |    1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index b038ec6..5bd4ef9 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -63,12 +63,13 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
>   * Check if any of the ctx, dispatch list or elevator
>   * have pending work in this hardware queue.
>   */
> -static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
> +bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
>  {
>  	return !list_empty_careful(&hctx->dispatch) ||
>  		sbitmap_any_bit_set(&hctx->ctx_map) ||
>  			blk_mq_sched_has_work(hctx);
>  }
> +EXPORT_SYMBOL_GPL(blk_mq_hctx_has_pending);

Just wondering why you don't use the 'last' field of 'struct blk_mq_queue_data',
which is passed to .queue_rq(), and supposed for implementing batch submission.
	

Thanks,
Ming