[PATCH] ufs: core: Use a host-wide tagset in SDB mode

[PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Bart Van Assche]

In single-doorbell (SDB) mode there is only a single request queue. Hence,
it doesn't matter whether or not the SCSI host tagset is configured as
host-wide. Configure the host tagset as host-wide in SDB mode because
this enables a simplification of the hot path.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/ufs/core/ufs-mcq.c     | 2 --
 drivers/ufs/core/ufshcd-priv.h | 7 +------
 drivers/ufs/core/ufshcd.c      | 1 +
 3 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/ufs/core/ufs-mcq.c b/drivers/ufs/core/ufs-mcq.c
index 64c234096e23..18a95b728633 100644
--- a/drivers/ufs/core/ufs-mcq.c
+++ b/drivers/ufs/core/ufs-mcq.c
@@ -444,7 +444,6 @@ EXPORT_SYMBOL_GPL(ufshcd_mcq_config_esi);
 
 int ufshcd_mcq_init(struct ufs_hba *hba)
 {
-	struct Scsi_Host *host = hba->host;
 	struct ufs_hw_queue *hwq;
 	int ret, i;
 
@@ -478,7 +477,6 @@ int ufshcd_mcq_init(struct ufs_hba *hba)
 		mutex_init(&hwq->sq_mutex);
 	}
 
-	host->host_tagset = 1;
 	return 0;
 }
 
diff --git a/drivers/ufs/core/ufshcd-priv.h b/drivers/ufs/core/ufshcd-priv.h
index 4259f499382f..7d6d19361af9 100644
--- a/drivers/ufs/core/ufshcd-priv.h
+++ b/drivers/ufs/core/ufshcd-priv.h
@@ -374,12 +374,7 @@ static inline bool ufs_is_valid_unit_desc_lun(struct ufs_dev_info *dev_info, u8
  */
 static inline struct scsi_cmnd *ufshcd_tag_to_cmd(struct ufs_hba *hba, u32 tag)
 {
-	/*
-	 * Host-wide tags are enabled in MCQ mode only. See also the
-	 * host->host_tagset assignment in ufs-mcq.c.
-	 */
-	struct blk_mq_tags *tags = hba->host->tag_set.shared_tags ?:
-					   hba->host->tag_set.tags[0];
+	struct blk_mq_tags *tags = hba->host->tag_set.shared_tags;
 	struct request *rq = blk_mq_tag_to_rq(tags, tag);
 
 	if (WARN_ON_ONCE(!rq))
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 057678f4c50a..889da15a61f0 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -9320,6 +9320,7 @@ static const struct scsi_host_template ufshcd_driver_template = {
 	.max_segment_size	= PRDT_DATA_BYTE_COUNT_MAX,
 	.max_sectors		= SZ_1M / SECTOR_SIZE,
 	.max_host_blocked	= 1,
+	.host_tagset		= true,
 	.track_queue_depth	= 1,
 	.skip_settle_delay	= 1,
 	.sdev_groups		= ufshcd_driver_groups,

Re: [PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Peter Wang (王信友)]

On Fri, 2026-01-16 at 10:07 -0800, Bart Van Assche wrote:
> In single-doorbell (SDB) mode there is only a single request queue.
> Hence,
> it doesn't matter whether or not the SCSI host tagset is configured
> as
> host-wide. Configure the host tagset as host-wide in SDB mode because
> this enables a simplification of the hot path.
> 

Hi Bart,

Would this affect the performance of the SDB mode?


> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 057678f4c50a..889da15a61f0 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -9320,6 +9320,7 @@ static const struct scsi_host_template
> ufshcd_driver_template = {
>         .max_segment_size       = PRDT_DATA_BYTE_COUNT_MAX,
>         .max_sectors            = SZ_1M / SECTOR_SIZE,
>         .max_host_blocked       = 1,
> +       .host_tagset            = true,

Should be = 1?

Thanks
Peter

>         .track_queue_depth      = 1,
>         .skip_settle_delay      = 1,
>         .sdev_groups            = ufshcd_driver_groups,

Re: [PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Bart Van Assche]

On 1/20/26 11:21 PM, Peter Wang (王信友) wrote:
> On Fri, 2026-01-16 at 10:07 -0800, Bart Van Assche wrote:
>> In single-doorbell (SDB) mode there is only a single request queue.
>> Hence,
>> it doesn't matter whether or not the SCSI host tagset is configured
>> as
>> host-wide. Configure the host tagset as host-wide in SDB mode because
>> this enables a simplification of the hot path.
> 
> Would this affect the performance of the SDB mode?

Hi Peter,

I reviewed all the blk_mq_is_shared_tags() calls in the block layer.
Based on that analysis I don't expect a measurable performance impact.

>> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
>> index 057678f4c50a..889da15a61f0 100644
>> --- a/drivers/ufs/core/ufshcd.c
>> +++ b/drivers/ufs/core/ufshcd.c
>> @@ -9320,6 +9320,7 @@ static const struct scsi_host_template
>> ufshcd_driver_template = {
>>         .max_segment_size       = PRDT_DATA_BYTE_COUNT_MAX,
>>         .max_sectors            = SZ_1M / SECTOR_SIZE,
>>         .max_host_blocked       = 1,
>> +       .host_tagset            = true,
> 
> Should be = 1?
.host_tagset is used as a boolean and the compiler converts 'true' into 
'1' if used as an integer so I think 'true' is fine.

Thanks,

Bart.

Re: [PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Peter Wang (王信友)]

On Wed, 2026-01-21 at 09:27 -0800, Bart Van Assche wrote:
> On 1/20/26 11:21 PM, Peter Wang (王信友) wrote:
> > On Fri, 2026-01-16 at 10:07 -0800, Bart Van Assche wrote:
> > > In single-doorbell (SDB) mode there is only a single request
> > > queue.
> > > Hence,
> > > it doesn't matter whether or not the SCSI host tagset is
> > > configured
> > > as
> > > host-wide. Configure the host tagset as host-wide in SDB mode
> > > because
> > > this enables a simplification of the hot path.
> > 
> > Would this affect the performance of the SDB mode?
> 
> Hi Peter,
> 
> I reviewed all the blk_mq_is_shared_tags() calls in the block layer.
> Based on that analysis I don't expect a measurable performance
> impact.
> 

Hi Bart,

After testing, it indeed does not impact performance.


> > > diff --git a/drivers/ufs/core/ufshcd.c
> > > b/drivers/ufs/core/ufshcd.c
> > > index 057678f4c50a..889da15a61f0 100644
> > > --- a/drivers/ufs/core/ufshcd.c
> > > +++ b/drivers/ufs/core/ufshcd.c
> > > @@ -9320,6 +9320,7 @@ static const struct scsi_host_template
> > > ufshcd_driver_template = {
> > >         .max_segment_size       = PRDT_DATA_BYTE_COUNT_MAX,
> > >         .max_sectors            = SZ_1M / SECTOR_SIZE,
> > >         .max_host_blocked       = 1,
> > > +       .host_tagset            = true,
> > 
> > Should be = 1?
> .host_tagset is used as a boolean and the compiler converts 'true'
> into
> '1' if used as an integer so I think 'true' is fine.
> 
> Thanks,
> 
> Bart.

Reviewed-by: Peter Wang <peter.wang@mediatek.com>

Re: [PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Martin K. Petersen]

Bart,

> In single-doorbell (SDB) mode there is only a single request queue.
> Hence, it doesn't matter whether or not the SCSI host tagset is
> configured as host-wide. Configure the host tagset as host-wide in SDB
> mode because this enables a simplification of the hot path.

Applied to 6.20/scsi-staging, thanks!

-- 
Martin K. Petersen

Re: [PATCH] ufs: core: Use a host-wide tagset in SDB mode

[Martin K. Petersen]

On Fri, 16 Jan 2026 10:07:51 -0800, Bart Van Assche wrote:

> In single-doorbell (SDB) mode there is only a single request queue. Hence,
> it doesn't matter whether or not the SCSI host tagset is configured as
> host-wide. Configure the host tagset as host-wide in SDB mode because
> this enables a simplification of the hot path.
> 
> 

Applied to 6.20/scsi-queue, thanks!

[1/1] ufs: core: Use a host-wide tagset in SDB mode
      https://git.kernel.org/mkp/scsi/c/4d0538dd5d7e

-- 
Martin K. Petersen