Re: [PATCH 01/12] blk-mq: do not include passthrough requests in I/O accounting

[Ming Lei <ming.lei@redhat.com>]

On Tue, Feb 22, 2022 at 03:14:39PM +0100, Christoph Hellwig wrote:
> I/O accounting buckets I/O into the read/write/discard categories into
> which passthrough I/O does not fit at all.  It also accounts to the
> block_device, which may not even exist for passthrough I/O.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/blk-mq.c | 6 +-----
>  block/blk.h    | 2 +-
>  2 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a05ce77250316..ee80853473d1e 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -883,11 +883,7 @@ static inline void blk_account_io_done(struct request *req, u64 now)
>  
>  static void __blk_account_io_start(struct request *rq)
>  {
> -	/* passthrough requests can hold bios that do not have ->bi_bdev set */
> -	if (rq->bio && rq->bio->bi_bdev)
> -		rq->part = rq->bio->bi_bdev;
> -	else if (rq->q->disk)
> -		rq->part = rq->q->disk->part0;
> +	rq->part = rq->bio->bi_bdev;
>  
>  	part_stat_lock();
>  	update_io_ticks(rq->part, jiffies, false);
> diff --git a/block/blk.h b/block/blk.h
> index ebaa59ca46ca6..6f21859c7f0ff 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -325,7 +325,7 @@ int blk_dev_init(void);
>   */
>  static inline bool blk_do_io_stat(struct request *rq)
>  {
> -	return (rq->rq_flags & RQF_IO_STAT) && rq->q->disk;
> +	return (rq->rq_flags & RQF_IO_STAT) && !blk_rq_is_passthrough(rq);

I guess this way may cause regression for workloads with lots of userspace IO
from user viewpoint?


Thanks,
Ming