Re: [PATCH] block: Submit flush requests to the I/O scheduler

[Bart Van Assche <bvanassche@xxxxxxx>]

On 8/14/22 10:13, Damien Le Moal wrote:
> And writes to zoned drives never get plugged in the first place, scheduler
> present or not.

Hi Damien,

I agree that blk_mq_submit_bio() does not plug writes to zoned drives 
because of the following code in blk_mq_plug():

/* Zoned block device write operation case: do not plug the BIO */
if (bdev_is_zoned(bio->bi_bdev) && op_is_write(bio_op(bio)))
	return NULL;

However, I have not found any code in blk_execute_rq_nowait() that 
causes the plugging mechanism to be skipped for zoned writes. Did I 
perhaps overlook something? The current blk_execute_rq_nowait() 
implementation is as follows:

void blk_execute_rq_nowait(struct request *rq, bool at_head)
{
	WARN_ON(irqs_disabled());
	WARN_ON(!blk_rq_is_passthrough(rq));

	blk_account_io_start(rq);
	if (current->plug)
		blk_add_rq_to_plug(current->plug, rq);
	else
		blk_mq_sched_insert_request(rq, at_head, true, false);
}

Thanks,

Bart.