On 5/17/23 16:47, Hannes Reinecke wrote:
> On 5/17/23 00:33, Bart Van Assche wrote:
>> Before dispatching a zoned write from the FIFO list, check whether there
>> are any zoned writes in the RB-tree with a lower LBA for the same zone.
>> This patch ensures that zoned writes happen in order even if at_head is
>> set for some writes for a zone and not for others.
>>
>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>> Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
>> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
>> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
>> ---
>> block/mq-deadline.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
>> index 059727fa4b98..67989f8d29a5 100644
>> --- a/block/mq-deadline.c
>> +++ b/block/mq-deadline.c
>> @@ -346,7 +346,7 @@ static struct request *
>> deadline_fifo_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
>> enum dd_data_dir data_dir)
>> {
>> - struct request *rq;
>> + struct request *rq, *rb_rq, *next;
>> unsigned long flags;
>>
>> if (list_empty(&per_prio->fifo_list[data_dir]))
>> @@ -364,7 +364,12 @@ deadline_fifo_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
>> * zones and these zones are unlocked.
>> */
>> spin_lock_irqsave(&dd->zone_lock, flags);
>> - list_for_each_entry(rq, &per_prio->fifo_list[DD_WRITE], queuelist) {
>> + list_for_each_entry_safe(rq, next, &per_prio->fifo_list[DD_WRITE],
>> + queuelist) {
>> + /* Check whether a prior request exists for the same zone. */
>> + rb_rq = deadline_from_pos(per_prio, data_dir, blk_rq_pos(rq));
>> + if (rb_rq && blk_rq_pos(rb_rq) < blk_rq_pos(rq))
>> + rq = rb_rq;
>> if (blk_req_can_dispatch_to_zone(rq) &&
>> (blk_queue_nonrot(rq->q) ||
>> !deadline_is_seq_write(dd, rq)))
>
> Similar concern here; we'll have to traverse the entire tree here.
> But if that's of no concern...
Should be fine for HDDs. Not so sure about much faster UFS devices.
And for NVMe ZNS, using a scheduler in itself already halve the max perf you can
get...
>
> Cheers,
>
> Hannes
--
Damien Le Moal
Western Digital Research
