Re: [PATCH v13 10/18] scsi: sd_zbc: Only require an I/O scheduler if needed

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

On 10/19/23 02:54, Bart Van Assche wrote:
> An I/O scheduler that serializes zoned writes is only needed if the SCSI
> LLD does not preserve the write order. Hence only set
> ELEVATOR_F_ZBD_SEQ_WRITE if the LLD does not preserve the write order.
> 
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> Cc: Martin K. Petersen <martin.petersen@oracle.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/scsi/sd_zbc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/sd_zbc.c b/drivers/scsi/sd_zbc.c
> index a25215507668..718b31bed878 100644
> --- a/drivers/scsi/sd_zbc.c
> +++ b/drivers/scsi/sd_zbc.c
> @@ -955,7 +955,9 @@ int sd_zbc_read_zones(struct scsi_disk *sdkp, u8 buf[SD_BUF_SIZE])
>  
>  	/* The drive satisfies the kernel restrictions: set it up */
>  	blk_queue_flag_set(QUEUE_FLAG_ZONE_RESETALL, q);
> -	blk_queue_required_elevator_features(q, ELEVATOR_F_ZBD_SEQ_WRITE);
> +	if (!q->limits.driver_preserves_write_order)

Where is this limit introduced ? I do not see it anywhere in your patches. Did I
miss something ?

> +		blk_queue_required_elevator_features(q,
> +						     ELEVATOR_F_ZBD_SEQ_WRITE);
>  	if (sdkp->zones_max_open == U32_MAX)
>  		disk_set_max_open_zones(disk, 0);
>  	else

-- 
Damien Le Moal
Western Digital Research