Re: [PATCH] scsi: sd: Add a comment about limiting max_sectors to shost optimal limit

Damien Le Moal
2022-07-19T10:06:56Z

On 7/19/22 18:51, John Garry wrote:
> Add a comment about limiting the default the SCSI disk request_queue
> max_sectors initial value to that of the SCSI host optimal sectors limit.
>
> Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Signed-off-by: John Garry <john.garry@huawei.com>
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 3eaee1f7aaca..ed9f43f9512e 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -3296,6 +3296,11 @@ static int sd_revalidate_disk(struct gendisk *disk)
> (sector_t)BLK_DEF_MAX_SECTORS);
> }
>
> + /*
> + * Limit default to SCSI host optimal sector limit if set. There may be
> + * an impact on performance for when the size of a request exceeds this
> + * host limit.
> + */
> rw_max = min_not_zero(rw_max, sdp->host->opt_sectors);
>
> /* Do not exceed controller limit */

Looks good.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

--
Damien Le Moal
Western Digital Research