Re: [PATCH V5 13/14] block: mq-deadline: Limit write request dispatch for zoned block devices

[Bart Van Assche <Bart.VanAssche@wdc.com>]

On Mon, 2017-09-25 at 15:14 +0900, Damien Le Moal wrote:
> -	return rq_entry_fifo(dd->fifo_list[data_dir].next);
> +	if (!dd->zones_wlock || data_dir == READ)
> +		return rq_entry_fifo(dd->fifo_list[data_dir].next);
> +
> +	spin_lock_irqsave(&dd->zone_lock, flags);
> +
> +	list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
> +		if (deadline_can_dispatch_request(dd, rq))
> +			goto out;
> +	}
> +	rq = NULL;
> +
> +out:
> +	spin_unlock_irqrestore(&dd->zone_lock, flags);

Is it documented somewhere what dd->zone_lock protects and when that lock should be
acquired?

> 	/*
>  	 * This may be a requeue of a request that has locked its
> -	 * target zone. If this is the case, release the request zone lock.
> +	 * target zone. If this is the case, release the zone lock.
>  	 */
>  	if (deadline_request_has_zone_wlock(rq))
>  		deadline_wunlock_zone(dd, rq);

Can this change be folded into the patch that introduced that comment?

> @@ -570,6 +621,9 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>  
>  	blk_mq_sched_request_inserted(rq);
>  
> +	if (at_head && deadline_request_needs_zone_wlock(dd, rq))
> +		pr_info("######## Write at head !\n");
> +
>  	if (at_head || blk_rq_is_passthrough(rq)) {
>  		if (at_head)
>  			list_add(&rq->queuelist, &dd->dispatch);

Will it be easy to users who analyze a kernel log to figure out why that
message has been generated? Should that message perhaps include the block
device name, zone number and request sector number?

Thanks,

Bart.