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

Damien Le Moal
2023-08-18T02:42:32Z

On 2023/08/17 23:34, Bart Van Assche wrote:
> 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?

This is called from scsi_eh_flush_done_q() which also does not have the scsi
device pointer. And places where this is called have the scsi host pointer, not
the device. OK. So let's no do that.

>
> Thanks,
>
> Bart.
>

--
Damien Le Moal
Western Digital Research