Re: [PATCH] blk-mq: use blk_mq_timeout_work to limit the max timeout

[Bart Van Assche]

On Tue, 2018-06-19 at 15:00 +0800, Jianchao Wang wrote:
> blk_rq_timeout is needed to limit the max timeout value, otherwise,
> a idle hctx cannot be deactivated timely in shared-tag case.
> 
> Fixes: 12f5b931 (blk-mq: Remove generation seqeunce)
> Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
> ---
>  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 70c65bb..ccebe7b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -868,7 +868,7 @@ static void blk_mq_timeout_work(struct work_struct *work)
>  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next);
>  
>  	if (next != 0) {
> -		mod_timer(&q->timeout, next);
> +		mod_timer(&q->timeout, blk_rq_timeout(round_jiffies_up(next)));
>  	} else {
>  		/*
>  		 * Request timeouts are handled as a forward rolling timer. If

Hello Jianchao,

What makes you think that it would be necessary to call blk_rq_timeout() from
blk_mq_timeout_work()? Have you noticed that blk_add_timer() already calls that
function? I think it is not necessary to call blk_rq_timeout() from
blk_mq_timeout_work() because it is guaranteed in that function that the next
timeout is less than BLK_MAX_TIMEOUT jiffies in the future.

Bart.