Re: [PATCH v4 3/7] block: Send requeued requests to the I/O scheduler

[Damien Le Moal <dlemoal@kernel.org>]

On 6/23/23 02:23, Bart Van Assche wrote:
> On 6/21/23 18:19, Damien Le Moal wrote:
>> Why ? I still do not understand the need for this. There is always only a single
>> in-flight write per sequential zone. Requeuing that in-flight write directly to
>> the dispatch list will not reorder writes and it will be better for the command
>> latency.
> Hi Damien,
> 
> After having taken a closer look I see that blk_req_zone_write_unlock() 
> is called from inside dd_insert_request() when requeuing a request. 
> Hence, there is no reordering risk when requeuing a zoned write. I will 
> drop this patch.

OK. Thanks.

> 
> Do you agree with having one requeue list per hctx instead of per 
> request queue? This change enables eliminating 
> blk_mq_kick_requeue_list(). I think that's an interesting simplification 
> of the block layer API.

I do not see any issue with that. Indeed, it does simplify the code nicely.
Reading patch 5, I wondered though if it is really worth keeping the helpers
blk_mq_kick_requeue_list() and blk_mq_delay_kick_requeue_list(). May be calling
blk_mq_run_hw_queues() and blk_mq_delay_run_hw_queues() is better ? No strong
opinion though.

-- 
Damien Le Moal
Western Digital Research