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author | Christoph Hellwig <hch@lst.de> | 2014-01-17 12:06:53 +0100 |
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committer | Christoph Hellwig <hch@lst.de> | 2014-07-25 17:16:28 -0400 |
commit | d285203cf647d7c97db3a1c33794315c9008593f (patch) | |
tree | a28a0a902cf3f467e326a02f5632b917b75c56a3 /drivers/scsi/scsi_priv.h | |
parent | c53c6d6a68b13b1dff2892551b56cfdc07887d9e (diff) | |
download | linux-d285203cf647d7c97db3a1c33794315c9008593f.tar.bz2 |
scsi: add support for a blk-mq based I/O path.
This patch adds support for an alternate I/O path in the scsi midlayer
which uses the blk-mq infrastructure instead of the legacy request code.
Use of blk-mq is fully transparent to drivers, although for now a host
template field is provided to opt out of blk-mq usage in case any unforseen
incompatibilities arise.
In general replacing the legacy request code with blk-mq is a simple and
mostly mechanical transformation. The biggest exception is the new code
that deals with the fact the I/O submissions in blk-mq must happen from
process context, which slightly complicates the I/O completion handler.
The second biggest differences is that blk-mq is build around the concept
of preallocated requests that also include driver specific data, which
in SCSI context means the scsi_cmnd structure. This completely avoids
dynamic memory allocations for the fast path through I/O submission.
Due the preallocated requests the MQ code path exclusively uses the
host-wide shared tag allocator instead of a per-LUN one. This only
affects drivers actually using the block layer provided tag allocator
instead of their own. Unlike the old path blk-mq always provides a tag,
although drivers don't have to use it.
For now the blk-mq path is disable by defauly and must be enabled using
the "use_blk_mq" module parameter. Once the remaining work in the block
layer to make blk-mq more suitable for slow devices is complete I hope
to make it the default and eventually even remove the old code path.
Based on the earlier scsi-mq prototype by Nicholas Bellinger.
Thanks to Bart Van Assche and Robert Elliot for testing, benchmarking and
various sugestions and code contributions.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
Diffstat (limited to 'drivers/scsi/scsi_priv.h')
-rw-r--r-- | drivers/scsi/scsi_priv.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h index a45d1c2eb414..12b8e1bee7f0 100644 --- a/drivers/scsi/scsi_priv.h +++ b/drivers/scsi/scsi_priv.h @@ -88,6 +88,9 @@ extern void scsi_next_command(struct scsi_cmnd *cmd); extern void scsi_io_completion(struct scsi_cmnd *, unsigned int); extern void scsi_run_host_queues(struct Scsi_Host *shost); extern struct request_queue *scsi_alloc_queue(struct scsi_device *sdev); +extern struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev); +extern int scsi_mq_setup_tags(struct Scsi_Host *shost); +extern void scsi_mq_destroy_tags(struct Scsi_Host *shost); extern int scsi_init_queue(void); extern void scsi_exit_queue(void); struct request_queue; |