linux-kernel - Re: [PATCH v2 5/5] block/null_blk: add queue

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Date:   Fri, 22 Sep 2023 16:54:47 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     chengming.zhou@...ux.dev
Cc:     axboe@...nel.dk, hch@....de, bvanassche@....org, kbusch@...nel.org,
        mst@...hat.com, damien.lemoal@...nsource.wdc.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH v2 5/5] block/null_blk: add queue_rqs() support

On Wed, Sep 13, 2023 at 03:16:16PM +0000, chengming.zhou@...ux.dev wrote:
> From: Chengming Zhou <zhouchengming@...edance.com>
> 
> Add batched mq_ops.queue_rqs() support in null_blk for testing. The
> implementation is much easy since null_blk doesn't have commit_rqs().
> 
> We simply handle each request one by one, if errors are encountered,
> leave them in the passed in list and return back.
> 
> There is about 3.6% improvement in IOPS of fio/t/io_uring on null_blk
> with hw_queue_depth=256 on my test VM, from 1.09M to 1.13M.

I guess you pass 'shared_tags' to null_blk for the verification?

> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  drivers/block/null_blk/main.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 968090935eb2..79d6cd3c3d41 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -1750,6 +1750,25 @@ static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	return null_handle_cmd(cmd, sector, nr_sectors, req_op(rq));
>  }
>  
> +static void null_queue_rqs(struct request **rqlist)
> +{
> +	struct request *requeue_list = NULL;
> +	struct request **requeue_lastp = &requeue_list;
> +	struct blk_mq_queue_data bd = { };
> +	blk_status_t ret;
> +
> +	do {
> +		struct request *rq = rq_list_pop(rqlist);
> +
> +		bd.rq = rq;
> +		ret = null_queue_rq(rq->mq_hctx, &bd);
> +		if (ret != BLK_STS_OK)
> +			rq_list_add_tail(&requeue_lastp, rq);
> +	} while (!rq_list_empty(*rqlist));
> +
> +	*rqlist = requeue_list;
> +}
> +

null_blk may not be one perfect example for showing queue_rqs()
which is usually for handling request in batch, but for test or
demo purpose, it is fine:

Reviewed-by: Ming Lei <ming.lei@...hat.com>


Thanks
Ming