Re: [PATCH 6/6] scsi: mvsas: Use sas_task_find_rq() for tagging

John Garry
2022-09-29T07:49:32Z

On 29/09/2022 03:22, Damien Le Moal wrote:
> On 9/28/22 21:27, John Garry wrote:
>> The request associated with a scsi command coming from the block layer
>> has a unique tag, so use that when possible for getting a slot.
>>
>> Unfortunately we don't support reserved commands in the SCSI midlayer yet.
>> As such, SMP tasks - as an example - will not have a request associated, so
>> in the interim continue to manage those tags for that type of sas_task
>> internally.
>>
>> We reserve an arbitrary 4 tags for these internal tags. Indeed, we already
>> decrement MVS_RSVD_SLOTS by 2 for the shost can_queue when flag
>> MVF_FLAG_SOC is set. This change was made in commit 20b09c2992fef
>> ("[PATCH] [SCSI] mvsas: add support for 94xx; layout change; bug fixes"),
>> but what those 2 slots are used for is not obvious.
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>> ---
>> drivers/scsi/mvsas/mv_defs.h | 1 +
>> drivers/scsi/mvsas/mv_init.c | 4 ++--
>> drivers/scsi/mvsas/mv_sas.c | 22 +++++++++++++++++-----
>> drivers/scsi/mvsas/mv_sas.h | 1 -
>> 4 files changed, 20 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/scsi/mvsas/mv_defs.h b/drivers/scsi/mvsas/mv_defs.h
>> index 7123a2efbf58..8ef174cd4d37 100644
>> --- a/drivers/scsi/mvsas/mv_defs.h
>> +++ b/drivers/scsi/mvsas/mv_defs.h
>> @@ -40,6 +40,7 @@ enum driver_configuration {
>> MVS_ATA_CMD_SZ = 96, /* SATA command table buffer size */
>> MVS_OAF_SZ = 64, /* Open address frame buffer size */
>> MVS_QUEUE_SIZE = 64, /* Support Queue depth */
>> + MVS_RSVD_SLOTS = 4,
>> MVS_SOC_CAN_QUEUE = MVS_SOC_SLOTS - 2,
>> };
>>
>> diff --git a/drivers/scsi/mvsas/mv_init.c b/drivers/scsi/mvsas/mv_init.c
>> index c85fb812ad43..d834ed9e8e4a 100644
>> --- a/drivers/scsi/mvsas/mv_init.c
>> +++ b/drivers/scsi/mvsas/mv_init.c
>> @@ -284,7 +284,7 @@ static int mvs_alloc(struct mvs_info *mvi, struct Scsi_Host *shost)
>> printk(KERN_DEBUG "failed to create dma pool %s.\n", pool_name);
>> goto err_out;
>> }
>> - mvi->tags_num = slot_nr;
>> + mvi->tags_num = MVS_RSVD_SLOTS;
>
> Same comment as for pm8001: do you really need this field if the value
> is always MVS_RSVD_SLOTS ?

Right, I don't need this struct member. Again I can just use this macro
directly.

>
>>
>> return 0;
>> err_out:
>> @@ -367,7 +367,7 @@ static struct mvs_info *mvs_pci_alloc(struct pci_dev *pdev,
>> mvi->sas = sha;
>> mvi->shost = shost;
>>
>> - mvi->tags = kzalloc(MVS_CHIP_SLOT_SZ>>3, GFP_KERNEL);
>> + mvi->tags = kzalloc(MVS_RSVD_SLOTS, GFP_KERNEL);
>
> Field name ? reserved_tags ?
> Also, the alloc seems wrong. This will allocate 4 bytes, but you only
> need 4 bits. You could make this an unsigned long and not allocate
> anything.

Well spotted. I should have questioned more why they had >>3 previously.

But I would rather keep as a bitmap, i.e. *unsigned long for simplicity.

> Same remark for pm8001 by the way.

I think it's ok as it uses bitmap_zalloc()

>
> That would cap MVS_RSVD_SLOTS to BITS_PER_LONG maximum, but that is easy
> to check at compile time with a #if/#error.
>

As above, I'd rather keep as a bitmap. It's a little inefficient, but is
a one off in the driver.

Thanks,
John