Re: [PATCH] blk-mq: update hctx->dispatch_busy in case of real scheduler

[Jan Kara <jack@suse.cz>]

On Fri 28-05-21 11:20:55, Ming Lei wrote:
> Commit 6e6fcbc27e77 ("blk-mq: support batching dispatch in case of io")
> starts to support io batching submission by using hctx->dispatch_busy.
> 
> However, blk_mq_update_dispatch_busy() isn't changed to update hctx->dispatch_busy
> in that commit, so fix the issue by updating hctx->dispatch_busy in case
> of real scheduler.
> 
> Reported-by: Jan Kara <jack@suse.cz>
> Fixes: 6e6fcbc27e77 ("blk-mq: support batching dispatch in case of io")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-mq.c | 3 ---
>  1 file changed, 3 deletions(-)

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

BTW: Do you plan to submit also your improvement to
__blk_mq_do_dispatch_sched() to update dispatch_busy during the fetching
requests from the scheduler to avoid draining all requests from the IO
scheduler?

								Honza
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f11d4018ce2e..4930f7119f22 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1224,9 +1224,6 @@ static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
>  {
>  	unsigned int ewma;
>  
> -	if (hctx->queue->elevator)
> -		return;
> -
>  	ewma = hctx->dispatch_busy;
>  
>  	if (!ewma && !busy)
> -- 
> 2.29.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR