On Thu, Apr 15, 2021 at 11:39:20AM +0800, Lin Feng wrote:
> Commit 01e99aeca39796003 ("blk-mq: insert passthrough request into
> hctx->dispatch directly") gives high priority to passthrough requests and
> bypass underlying IO scheduler. But as we allocate tag for such request it
> still runs io-scheduler's callback limit_depth, while we really want is to
> give full sbitmap-depth capabity to such request for acquiring available
> tag.
> blktrace shows PC requests(dmraid -s -c -i) hit bfq's limit_depth:
> 8,0 2 0 0.000000000 39952 1,0 m N bfq [bfq_limit_depth] wr_busy 0 sync 0 depth 8
> 8,0 2 1 0.000008134 39952 D R 4 [dmraid]
> 8,0 2 2 0.000021538 24 C R [0]
> 8,0 2 0 0.000035442 39952 1,0 m N bfq [bfq_limit_depth] wr_busy 0 sync 0 depth 8
> 8,0 2 3 0.000038813 39952 D R 24 [dmraid]
> 8,0 2 4 0.000044356 24 C R [0]
>
> This patch introduce a new wrapper to make code not that ugly.
>
> Signed-off-by: Lin Feng <linf@xxxxxxxxxx>
> ---
> block/blk-mq.c | 3 ++-
> include/linux/blkdev.h | 6 ++++++
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d4d7c1caa439..927189a55575 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -361,11 +361,12 @@ static struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data)
>
> if (e) {
> /*
> - * Flush requests are special and go directly to the
> + * Flush/passthrough requests are special and go directly to the
> * dispatch list. Don't include reserved tags in the
> * limiting, as it isn't useful.
> */
> if (!op_is_flush(data->cmd_flags) &&
> + !blk_op_is_passthrough(data->cmd_flags) &&
> e->type->ops.limit_depth &&
> !(data->flags & BLK_MQ_REQ_RESERVED))
> e->type->ops.limit_depth(data->cmd_flags, data);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 158aefae1030..0d81eed39833 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -272,6 +272,12 @@ static inline bool bio_is_passthrough(struct bio *bio)
> return blk_op_is_scsi(op) || blk_op_is_private(op);
> }
>
> +static inline bool blk_op_is_passthrough(unsigned int op)
> +{
> + return (blk_op_is_scsi(op & REQ_OP_MASK) ||
> + blk_op_is_private(op & REQ_OP_MASK));
> +}
> +
> static inline unsigned short req_get_ioprio(struct request *req)
> {
> return req->ioprio;
> --
> 2.30.2
>
Looks fine:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
