Re: [PATCH RFC v3 0/8] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs

[John Garry <john.garry@huawei.com>]

On 26/11/2019 09:14, Hannes Reinecke wrote:
> Hi all,
> 
> here now is an updated version of the v2 patchset from John Garry,
> including the suggestions and reviews from the mailing list.
> John, apologies for hijacking your work :-)

No worries as long as we can keep moving this forward.

> 
> The main diffence is that I've changed the bitmaps to be allocated
> separately in all cases, and just set the pointer to the shared bitmap
> for the hostwide tags case.

Yeah, I was considering this also.

> I've also modified smartpqi and hpsa to take advantage of host_tags.
> 
> I did audit the iterators, and I _think_ they do the correct thing even
> in the shared bitmap case. But then I might have overlooked things,
> so feedback and reviews are welcome.
> 
> The one thing I'm not happy with is the debugfs interface; for shared
> bitmaps all will be displaying essentially the same information, which
> could be moved to a top-level directory. But that would change the
> layout and I'm not sure if that buys us anything.

I was having a look at this. I'd say we need to still show which bits 
are set per hctx.

Maybe we can do something like this:

a. In hctx_tags_bitmaphow() or other relevant functions, copy shared 
sbitmap map into temp sbitmap map (maybe even the per-hctx sbitmap)
b. iterate over to unset bits not relevant to hctx in temp sbitmap map
c. then do sbitmap_show

Locking may be a bit tricky.

Thanks,
John

> 
> Differences to v2:
> - Drop embedded tag bitmaps
> - Do not share scheduling tags
> - Add patches for hpsa and smartpqi
> 
> Differences to v1:
> - Use a shared sbitmap, and not a separate shared tags (a big change!)
> 	- Drop request.shared_tag
> - Add RB tags
> 
> Hannes Reinecke (4):
>    blk-mq: Use a pointer for sbitmap
>    scsi: Add template flag 'host_tagset'
>    smartpqi: enable host tagset
>    hpsa: switch to using blk-mq
> 
> John Garry (3):
>    blk-mq: Remove some unused function arguments
>    blk-mq: Facilitate a shared sbitmap per tagset
>    scsi: hisi_sas: Switch v3 hw to MQ
> 
> Ming Lei (1):
>    blk-mq: rename BLK_MQ_F_TAG_SHARED as BLK_MQ_F_TAG_QUEUE_SHARED
> 
>   block/bfq-iosched.c                    |   4 +-
>   block/blk-mq-debugfs.c                 |  10 ++--
>   block/blk-mq-sched.c                   |   8 ++-
>   block/blk-mq-tag.c                     | 104 ++++++++++++++++++++++-----------
>   block/blk-mq-tag.h                     |  18 +++---
>   block/blk-mq.c                         |  80 ++++++++++++++++---------
>   block/blk-mq.h                         |   9 ++-
>   block/kyber-iosched.c                  |   4 +-
>   drivers/scsi/hisi_sas/hisi_sas.h       |   3 +-
>   drivers/scsi/hisi_sas/hisi_sas_main.c  |  36 ++++++------
>   drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |  86 +++++++++++----------------
>   drivers/scsi/hpsa.c                    |  44 +++-----------
>   drivers/scsi/hpsa.h                    |   1 -
>   drivers/scsi/scsi_lib.c                |   2 +
>   drivers/scsi/smartpqi/smartpqi_init.c  |  38 ++++++++----
>   include/linux/blk-mq.h                 |   9 ++-
>   include/scsi/scsi_host.h               |   3 +
>   17 files changed, 260 insertions(+), 199 deletions(-)
>