[dm-devel] [PATCH V6 10/12] block: limit hw queues to be polled in each blk_poll()

[Hannes Reinecke]

On 4/22/21 2:20 PM, Ming Lei wrote:
> Limit at most 8 queues are polled in each blk_pull(), avoid to
> add extra latency when queue depth is high.
> 
> Reviewed-by: Jeffle Xu <jefflexu at linux.alibaba.com>
> Signed-off-by: Ming Lei <ming.lei at redhat.com>
> ---
>  block/blk-poll.c | 78 ++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 55 insertions(+), 23 deletions(-)
> 
> diff --git a/block/blk-poll.c b/block/blk-poll.c
> index 249d73ff6f81..20e7c47cc984 100644
> --- a/block/blk-poll.c
> +++ b/block/blk-poll.c
> @@ -288,36 +288,32 @@ static void bio_grp_list_move(struct bio_grp_list *dst,
>  	src->nr_grps -= cnt;
>  }
>  
> -static int blk_mq_poll_io(struct bio *bio)
> +#define POLL_HCTX_MAX_CNT 8
> +
> +static bool blk_add_unique_hctx(struct blk_mq_hw_ctx **data, int *cnt,
> +		struct blk_mq_hw_ctx *hctx)
>  {
> -	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> -	blk_qc_t cookie = bio_get_poll_data(bio);
> -	int ret = 0;
> +	int i;
>  
> -	/* wait until the bio is submitted really */
> -	if (!blk_qc_t_ready(cookie))
> -		return 0;
>  
> -	if (!bio_flagged(bio, BIO_DONE) && blk_qc_t_valid(cookie)) {
> -		struct blk_mq_hw_ctx *hctx =
> -			q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
> +	for (i = 0; i < *cnt; i++) {
> +		if (data[i] == hctx)
> +			goto exit;
> +	}
>  
> -		ret += blk_mq_poll_hctx(q, hctx);
> +	if (i < POLL_HCTX_MAX_CNT) {
> +		data[i] = hctx;
> +		(*cnt)++;
>  	}
> -	return ret;
> + exit:
> +	return *cnt == POLL_HCTX_MAX_CNT;
>  }
>  
> -static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
> +static void blk_build_poll_queues(struct bio_grp_list *grps,
> +		struct blk_mq_hw_ctx **data, int *cnt)
>  {
> -	int ret = 0;
>  	int i;
>  
> -	/*
> -	 * Poll hw queue first.
> -	 *
> -	 * TODO: limit max poll times and make sure to not poll same
> -	 * hw queue one more time.
> -	 */
>  	for (i = 0; i < grps->nr_grps; i++) {
>  		struct bio_grp_list_data *grp = &grps->head[i];
>  		struct bio *bio;
> @@ -325,11 +321,31 @@ static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
>  		if (bio_grp_list_grp_empty(grp))
>  			continue;
>  
> -		for (bio = grp->list.head; bio; bio = bio->bi_poll)
> -			ret += blk_mq_poll_io(bio);
> +		for (bio = grp->list.head; bio; bio = bio->bi_poll) {
> +			blk_qc_t  cookie;
> +			struct blk_mq_hw_ctx *hctx;
> +			struct request_queue *q;
> +
> +			if (bio_flagged(bio, BIO_DONE))
> +				continue;
> +
> +			/* wait until the bio is submitted really */
> +			cookie = bio_get_poll_data(bio);
> +			if (!blk_qc_t_ready(cookie) || !blk_qc_t_valid(cookie))
> +				continue;
> +
> +			q = bio->bi_bdev->bd_disk->queue;
> +			hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
> +			if (blk_add_unique_hctx(data, cnt, hctx))
> +				return;
> +		}
>  	}
> +}
> +
> +static void blk_bio_poll_reap_ios(struct bio_grp_list *grps)
> +{
> +	int i;
>  
> -	/* reap bios */
>  	for (i = 0; i < grps->nr_grps; i++) {
>  		struct bio_grp_list_data *grp = &grps->head[i];
>  		struct bio *bio;
> @@ -354,6 +370,22 @@ static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
>  		}
>  		__bio_grp_list_merge(&grp->list, &bl);
>  	}
> +}
> +
> +static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
> +{
> +	int ret = 0;
> +	int i;
> +	struct blk_mq_hw_ctx *hctx[POLL_HCTX_MAX_CNT];
> +	int cnt = 0;
> +
> +	blk_build_poll_queues(grps, hctx, &cnt);
> +
> +	for (i = 0; i < cnt; i++)
> +		ret += blk_mq_poll_hctx(hctx[i]->queue, hctx[i]);
> +
> +	blk_bio_poll_reap_ios(grps);
> +
>  	return ret;
>  }
>  
> 
Can't we make it a sysfs attribute instead of hard-coding it?
'8' seems a bit arbitrary to me, I'd rather have the ability to modify it...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		        Kernel Storage Architect
hare at suse.de			               +49 911 74053 688
SUSE Software Solutions Germany GmbH, 90409 Nürnberg
GF: F. Imendörffer, HRB 36809 (AG Nürnberg)