linux-kernel - Re: [RFC PATCH 2/2] bfq/mq-deadline: remove redundant check for passthrough request

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Date:   Fri, 16 Apr 2021 10:14:48 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Lin Feng <linf@...gsu.com>
Cc:     axboe@...nel.dk, paolo.valente@...aro.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] bfq/mq-deadline: remove redundant check for
 passthrough request

On Thu, Apr 15, 2021 at 11:43:26AM +0800, Lin Feng wrote:
> Since commit 01e99aeca39796003 'blk-mq: insert passthrough request into
> hctx->dispatch directly', passthrough request should not appear in
> IO-scheduler any more, so blk_rq_is_passthrough checking in addon IO
> schedulers is redundant.
> 
> (Notes: this patch passes generic IO load test with hdds under SAS
> controller and hdds under AHCI controller but obviously not covers all.
> Not sure if passthrough request can still escape into IO scheduler from
> blk_mq_sched_insert_requests, which is used by blk_mq_flush_plug_list and
> has lots of indirect callers.)
> 
> Signed-off-by: Lin Feng <linf@...gsu.com>
> ---
>  block/bfq-iosched.c | 2 +-
>  block/mq-deadline.c | 7 ++-----
>  2 files changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 95586137194e..b827c9212b02 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5627,7 +5627,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>  
>  	spin_lock_irq(&bfqd->lock);
>  	bfqq = bfq_init_rq(rq);
> -	if (!bfqq || at_head || blk_rq_is_passthrough(rq)) {
> +	if (!bfqq || at_head) {
>  		if (at_head)
>  			list_add(&rq->queuelist, &bfqd->dispatch);
>  		else
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index f3631a287466..04aded71ead2 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -500,11 +500,8 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>  
>  	trace_block_rq_insert(rq);
>  
> -	if (at_head || blk_rq_is_passthrough(rq)) {
> -		if (at_head)
> -			list_add(&rq->queuelist, &dd->dispatch);
> -		else
> -			list_add_tail(&rq->queuelist, &dd->dispatch);
> +	if (at_head) {
> +		list_add(&rq->queuelist, &dd->dispatch);
>  	} else {
>  		deadline_add_rq_rb(dd, rq);
>  
> -- 
> 2.30.2
> 

Looks fine:

Reviewed-by: Ming Lei <ming.lei@...hat.com>

Thanks,
Ming