Re: [PATCH] block: Fix inflight statistic for MQ submission with !elevator

[Ming Lei <tom.leiming@gmail.com>]

On Mon, Aug 31, 2020 at 11:37 PM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> According to Documentation/block/stat.rst, inflight should not include
> I/O requests that are in the queue but not yet dispatched to the device,
> but blk-mq identifies as inflight any request that has a tag allocated,
> which, for queues without elevator, happens at request allocation time
> and before it is queued in the ctx (default case in blk_mq_submit_bio).
>
> A more precise approach would be to only consider requests with state
> MQ_RQ_IN_FLIGHT.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> ---
>  block/blk-mq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 0015a1892153..997b3327eaa8 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -105,7 +105,7 @@ static bool blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx,
>  {
>         struct mq_inflight *mi = priv;
>
> -       if (rq->part == mi->part)
> +       if (rq->part == mi->part && rq->state == MQ_RQ_IN_FLIGHT)
>                 mi->inflight[rq_data_dir(rq)]++;

The fix looks fine. However, we have helper of
blk_mq_request_started() for this purpose.


Thanks,
Ming Lei