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

Damien Le Moal
2022-09-29T02:22:54Z

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 ?

>
> 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. Same remark for pm8001 by the way.

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

> if (!mvi->tags)
> goto err_out;
>
> diff --git a/drivers/scsi/mvsas/mv_sas.c b/drivers/scsi/mvsas/mv_sas.c
> index 0810e6c930e1..549d2ec89f60 100644
> --- a/drivers/scsi/mvsas/mv_sas.c
> +++ b/drivers/scsi/mvsas/mv_sas.c
> @@ -20,7 +20,7 @@ static int mvs_find_tag(struct mvs_info *mvi, struct sas_task *task, u32 *tag)
> return 0;
> }
>
> -void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
> +static void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
> {
> void *bitmap = mvi->tags;
> clear_bit(tag, bitmap);
> @@ -28,6 +28,11 @@ void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
>
> void mvs_tag_free(struct mvs_info *mvi, u32 tag)
> {
> + if (tag < mvi->shost->can_queue)
> + return;
> +
> + tag -= mvi->shost->can_queue;
> +
> mvs_tag_clear(mvi, tag);
> }
>
> @@ -47,6 +52,7 @@ inline int mvs_tag_alloc(struct mvs_info *mvi, u32 *tag_out)
> if (tag >= mvi->tags_num)
> return -SAS_QUEUE_FULL;
> mvs_tag_set(mvi, tag);
> + tag += mvi->shost->can_queue;
> *tag_out = tag;
> return 0;
> }
> @@ -696,6 +702,7 @@ static int mvs_task_prep(struct sas_task *task, struct mvs_info *mvi, int is_tmf
> struct mvs_task_exec_info tei;
> struct mvs_slot_info *slot;
> u32 tag = 0xdeadbeef, n_elem = 0;
> + struct request *rq;
> int rc = 0;
>
> if (!dev->port) {
> @@ -760,9 +767,14 @@ static int mvs_task_prep(struct sas_task *task, struct mvs_info *mvi, int is_tmf
> n_elem = task->num_scatter;
> }
>
> - rc = mvs_tag_alloc(mvi, &tag);
> - if (rc)
> - goto err_out;
> + rq = sas_task_find_rq(task);
> + if (rq) {
> + tag = rq->tag;
> + } else {
> + rc = mvs_tag_alloc(mvi, &tag);
> + if (rc)
> + goto err_out;
> + }
>
> slot = &mvi->slot_info[tag];
>
> @@ -857,7 +869,7 @@ int mvs_queue_command(struct sas_task *task, gfp_t gfp_flags)
> static void mvs_slot_free(struct mvs_info *mvi, u32 rx_desc)
> {
> u32 slot_idx = rx_desc & RXQ_SLOT_MASK;
> - mvs_tag_clear(mvi, slot_idx);
> + mvs_tag_free(mvi, slot_idx);
> }
>
> static void mvs_slot_task_free(struct mvs_info *mvi, struct sas_task *task,
> diff --git a/drivers/scsi/mvsas/mv_sas.h b/drivers/scsi/mvsas/mv_sas.h
> index fe57665bdb50..e6c70786ded9 100644
> --- a/drivers/scsi/mvsas/mv_sas.h
> +++ b/drivers/scsi/mvsas/mv_sas.h
> @@ -424,7 +424,6 @@ struct mvs_task_exec_info {
>
> /******************** function prototype *********************/
> void mvs_get_sas_addr(void *buf, u32 buflen);
> -void mvs_tag_clear(struct mvs_info *mvi, u32 tag);
> void mvs_tag_free(struct mvs_info *mvi, u32 tag);
> void mvs_tag_set(struct mvs_info *mvi, unsigned int tag);
> int mvs_tag_alloc(struct mvs_info *mvi, u32 *tag_out);

--
Damien Le Moal
Western Digital Research