Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & introduce force_blk_mq

Ming Lei
2018-02-05T10:23:43Z

On Mon, Feb 05, 2018 at 07:58:29AM +0100, Hannes Reinecke wrote:
> On 02/03/2018 05:21 AM, Ming Lei wrote:
> > Hi All,
> >
> > This patchset supports global tags which was started by Hannes originally:
> >
> > https://marc.info/?l=linux-block&m=149132580511346&w=2
> >
> > Also inroduce 'force_blk_mq' to 'struct scsi_host_template', so that
> > driver can avoid to support two IO paths(legacy and blk-mq), especially
> > recent discusion mentioned that SCSI_MQ will be enabled at default soon.
> >
> > https://marc.info/?l=linux-scsi&m=151727684915589&w=2
> >
> > With the above two changes, it should be easier to convert SCSI drivers'
> > reply queue into blk-mq's hctx, then the automatic irq affinity issue can
> > be solved easily, please see detailed descrption in commit log.
> >
> > Also drivers may require to complete request on the submission CPU
> > for avoiding hard/soft deadlock, which can be done easily with blk_mq
> > too.
> >
> > https://marc.info/?t=151601851400001&r=1&w=2
> >
> > The final patch uses the introduced 'force_blk_mq' to fix virtio_scsi
> > so that IO hang issue can be avoided inside legacy IO path, this issue is
> > a bit generic, at least HPSA/virtio-scsi are found broken with v4.15+.
> >
> > Thanks
> > Ming
> >
> > Ming Lei (5):
> > blk-mq: tags: define several fields of tags as pointer
> > blk-mq: introduce BLK_MQ_F_GLOBAL_TAGS
> > block: null_blk: introduce module parameter of 'g_global_tags'
> > scsi: introduce force_blk_mq
> > scsi: virtio_scsi: fix IO hang by irq vector automatic affinity
> >
> > block/bfq-iosched.c | 4 +--
> > block/blk-mq-debugfs.c | 11 ++++----
> > block/blk-mq-sched.c | 2 +-
> > block/blk-mq-tag.c | 67 +++++++++++++++++++++++++++++-----------------
> > block/blk-mq-tag.h | 15 ++++++++---
> > block/blk-mq.c | 31 ++++++++++++++++-----
> > block/blk-mq.h | 3 ++-
> > block/kyber-iosched.c | 2 +-
> > drivers/block/null_blk.c | 6 +++++
> > drivers/scsi/hosts.c | 1 +
> > drivers/scsi/virtio_scsi.c | 59 +++-------------------------------------
> > include/linux/blk-mq.h | 2 ++
> > include/scsi/scsi_host.h | 3 +++
> > 13 files changed, 105 insertions(+), 101 deletions(-)
> >
> Thanks Ming for picking this up.
>
> I'll give it a shot and see how it behaves on other hardware.

Hi Hannes,

Thanks for looking at it.

I am working on V2, which has fixed some issues, and added your patch
of 'scsi: Add template flag 'host_tagset', but causes a HPSA kernel
oops. Once it is fixed, I will posted V2 out, then there will be one
real example about how to use global tags for converting reply queue
to blk-mq hctx.

https://github.com/ming1/linux/commits/v4.15-for-next-global-tags-V2

Thanks,
Ming