Re: [PATCH v9 06/17] scsi: sd: Sort commands by LBA before resubmitting

Bart Van Assche
2023-08-17T14:35:27Z

On 8/17/23 04:13, Damien Le Moal wrote:
> On 8/17/23 04:53, Bart Van Assche wrote:
>> +static int sd_cmp_sector(void *priv, const struct list_head *_a,
>> + const struct list_head *_b)
>> +{
>> + struct scsi_cmnd *a = list_entry(_a, typeof(*a), eh_entry);
>> + struct scsi_cmnd *b = list_entry(_b, typeof(*b), eh_entry);
>> + struct request *rq_a = scsi_cmd_to_rq(a);
>> + struct request *rq_b = scsi_cmd_to_rq(b);
>> + bool use_zwl_a = rq_a->q->limits.use_zone_write_lock;
>> + bool use_zwl_b = rq_b->q->limits.use_zone_write_lock;
>> +
>> + /*
>> + * Order the commands that need zone write locking after the commands
>> + * that do not need zone write locking. Order the commands that do not
>> + * need zone write locking by LBA. Do not reorder the commands that
>> + * need zone write locking. See also the comment above the list_sort()
>> + * definition.
>> + */
>> + if (use_zwl_a || use_zwl_b)
>> + return use_zwl_a > use_zwl_b;
>> + return blk_rq_pos(rq_a) > blk_rq_pos(rq_b);
>> +}
>> +
>> +static void sd_prepare_resubmit(struct list_head *cmd_list)
>> +{
>> + /*
>> + * Sort pending SCSI commands in starting sector order. This is
>> + * important if one of the SCSI devices associated with @shost is a
>> + * zoned block device for which zone write locking is disabled.
>> + */
>> + list_sort(NULL, cmd_list, sd_cmp_sector);
>
> We should not need to do this for regular devices or zoned devices using zone
> write locking. So returning doing nothing would be better but the callback
> lacks a pointer to the scsi_device to test that.

@cmd_list may include SCSI commands for multiple SCSI devices so I'm not
sure which SCSI device pointer you are referring to in the above comment?

Thanks,

Bart.