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

From: Ming Lei <ming.lei@redhat.com>
To: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	Mike Snitzer <snitzer@redhat.com>,
	linux-scsi@vger.kernel.org, Arun Easi <arun.easi@cavium.com>,
	Omar Sandoval <osandov@fb.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	James Bottomley <james.bottomley@hansenpartnership.com>,
	Christoph Hellwig <hch@lst.de>,
	Don Brace <don.brace@microsemi.com>,
	Kashyap Desai <kashyap.desai@broadcom.com>,
	Peter Rivera <peter.rivera@broadcom.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Laurence Oberman <loberman@redhat.com>
Subject: Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & introduce force_blk_mq
Date: Mon, 5 Feb 2018 18:23:43 +0800	[thread overview]
Message-ID: <20180205102342.GB32558@ming.t460p> (raw)
In-Reply-To: <07c1f41e-de7c-5e3d-1a2d-0cd7af7b46df@suse.de>

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