From: Mike Snitzer <snitzer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>,
linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
dm-devel@redhat.com
Subject: Re: RFC: split scsi passthrough fields out of struct request
Date: Wed, 11 Jan 2017 17:41:42 -0500 [thread overview]
Message-ID: <20170111224142.GA19238@redhat.com> (raw)
In-Reply-To: <1484060780-15592-1-git-send-email-hch@lst.de>
On Tue, Jan 10 2017 at 10:06am -0500,
Christoph Hellwig <hch@lst.de> wrote:
> Hi all,
>
> this series splits the support for SCSI passthrough commands from the
> main struct request used all over the block layer into a separate
> scsi_request structure that drivers that want to support SCSI passthough
> need to embedded as the first thing into their request-private data,
> similar to how we handle NVMe passthrough commands.
>
> To support this I've added support for that the private data after
> request structure to the legacy request path instead, so that it can
> be treated the same way as the blk-mq path. Compare to the current
> scsi_cmnd allocator that actually is a major simplification.
>
> There is one major show-stopper for the series as-is: Request-based
> device mapper currently allocate the request structures in the stacking
> driver without a knowledge of the queue it's going to be submitte on
> for the legacy request path. It managed to avoid that issue for the
> blk-mq path, but that currently can't be used on legacy request devices
> for reasons I don't fully understand. We'll need to figure out how
> sort this out, but maybe that's a good opportunity to drop one or two
> of the three different dm-mpath I/O paths? :)
Ah, should've read the 0th patch earlier..
I removed blk-mq on request_fn paths support because it was one of the
permutations that I felt least useful/stable (see commit c5248f79f3 "dm:
remove support for stacking dm-mq on .request_fn device(s)")
As for all of the different IO paths. I've always liked the idea of
blk-mq ruling the world. With Jens' blk-mq IO scheduling advances maybe
we're closer!
next prev parent reply other threads:[~2017-01-11 22:41 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 15:06 RFC: split scsi passthrough fields out of struct request Christoph Hellwig
2017-01-10 15:06 ` [PATCH 01/15] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig
2017-01-11 8:26 ` Johannes Thumshirn
2017-01-11 8:26 ` Johannes Thumshirn
2017-01-11 8:43 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 02/15] nvme-rdma: fix nvme_rdma_queue_is_ready Christoph Hellwig
2017-01-10 15:06 ` [PATCH 03/15] block: simplify blk_init_allocated_queue Christoph Hellwig
2017-01-10 15:06 ` [PATCH 04/15] block: allow specifying size for extra command data Christoph Hellwig
2017-01-10 15:06 ` [PATCH 05/15] dm: remove incomple BLOCK_PC support Christoph Hellwig
2017-01-12 1:09 ` Mike Snitzer
2017-01-12 8:00 ` Christoph Hellwig
2017-01-12 22:28 ` Mike Snitzer
2017-01-13 8:14 ` Christoph Hellwig
2017-01-13 8:14 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 06/15] scsi_dh_rdac: switch to scsi_execute_req_flags() Christoph Hellwig
2017-01-10 15:06 ` [PATCH 07/15] scsi_dh_emc: " Christoph Hellwig
2017-01-10 15:06 ` [PATCH 08/15] scsi_dh_hp_sw: " Christoph Hellwig
2017-01-10 15:06 ` [PATCH 09/15] scsi: remove gfp_flags member in scsi_host_cmd_pool Christoph Hellwig
2017-01-10 15:06 ` [PATCH 10/15] scsi: respect unchecked_isa_dma for blk-mq Christoph Hellwig
2017-01-10 15:06 ` [PATCH 11/15] scsi: remove scsi_cmd_dma_pool Christoph Hellwig
2017-01-10 15:06 ` [PATCH 12/15] scsi: remove __scsi_alloc_queue Christoph Hellwig
2017-01-10 15:06 ` [PATCH 13/15] scsi: allocate scsi_cmnd structures as part of struct request Christoph Hellwig
2017-01-10 15:06 ` [PATCH 14/15] block/bsg: move queue creation into bsg_setup_queue Christoph Hellwig
2017-01-11 8:42 ` Johannes Thumshirn
2017-01-11 8:42 ` Johannes Thumshirn
2017-01-11 8:45 ` Christoph Hellwig
2017-01-11 8:56 ` Johannes Thumshirn
2017-01-11 8:56 ` Johannes Thumshirn
2017-01-11 8:59 ` Christoph Hellwig
2017-01-11 8:59 ` Hannes Reinecke
2017-01-11 8:59 ` Hannes Reinecke
2017-01-11 9:01 ` Christoph Hellwig
2017-01-11 9:37 ` Hannes Reinecke
2017-01-11 9:37 ` Hannes Reinecke
2017-01-11 22:08 ` Mike Snitzer
2017-01-11 22:01 ` Mike Snitzer
2017-01-12 7:57 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 15/15] block: split scsi_request out of struct request Christoph Hellwig
2017-01-12 3:59 ` Jens Axboe
2017-01-12 3:59 ` Jens Axboe
2017-01-11 22:41 ` Mike Snitzer [this message]
2017-01-12 7:59 ` RFC: split scsi passthrough fields " Christoph Hellwig
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