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

Hannes Reinecke
2021-04-26T07:19:32Z

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@linux.alibaba.com>
> Signed-off-by: Ming Lei <ming.lei@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@suse.de +49 911 74053 688
SUSE Software Solutions Germany GmbH, 90409 Nürnberg
GF: F. Imendörffer, HRB 36809 (AG Nürnberg)