linux/include/scsi/scsi_tcq.h
Christoph Hellwig d285203cf6 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>
2014-07-25 17:16:28 -04:00

198 lines
4.7 KiB
C

#ifndef _SCSI_SCSI_TCQ_H
#define _SCSI_SCSI_TCQ_H
#include <linux/blkdev.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_host.h>
#define MSG_SIMPLE_TAG 0x20
#define MSG_HEAD_TAG 0x21
#define MSG_ORDERED_TAG 0x22
#define MSG_ACA_TAG 0x24 /* unsupported */
#define SCSI_NO_TAG (-1) /* identify no tag in use */
#ifdef CONFIG_BLOCK
/**
* scsi_get_tag_type - get the type of tag the device supports
* @sdev: the scsi device
*
* Notes:
* If the drive only supports simple tags, returns MSG_SIMPLE_TAG
* if it supports all tag types, returns MSG_ORDERED_TAG.
*/
static inline int scsi_get_tag_type(struct scsi_device *sdev)
{
if (!sdev->tagged_supported)
return 0;
if (sdev->ordered_tags)
return MSG_ORDERED_TAG;
if (sdev->simple_tags)
return MSG_SIMPLE_TAG;
return 0;
}
static inline void scsi_set_tag_type(struct scsi_device *sdev, int tag)
{
switch (tag) {
case MSG_ORDERED_TAG:
sdev->ordered_tags = 1;
/* fall through */
case MSG_SIMPLE_TAG:
sdev->simple_tags = 1;
break;
case 0:
/* fall through */
default:
sdev->ordered_tags = 0;
sdev->simple_tags = 0;
break;
}
}
/**
* scsi_activate_tcq - turn on tag command queueing
* @SDpnt: device to turn on TCQ for
* @depth: queue depth
*
* Notes:
* Eventually, I hope depth would be the maximum depth
* the device could cope with and the real queue depth
* would be adjustable from 0 to depth.
**/
static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
{
if (!sdev->tagged_supported)
return;
if (!shost_use_blk_mq(sdev->host) &&
blk_queue_tagged(sdev->request_queue))
blk_queue_init_tags(sdev->request_queue, depth,
sdev->host->bqt);
scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
}
/**
* scsi_deactivate_tcq - turn off tag command queueing
* @SDpnt: device to turn off TCQ for
**/
static inline void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)
{
if (!shost_use_blk_mq(sdev->host) &&
blk_queue_tagged(sdev->request_queue))
blk_queue_free_tags(sdev->request_queue);
scsi_adjust_queue_depth(sdev, 0, depth);
}
/**
* scsi_populate_tag_msg - place a tag message in a buffer
* @SCpnt: pointer to the Scsi_Cmnd for the tag
* @msg: pointer to the area to place the tag
*
* Notes:
* designed to create the correct type of tag message for the
* particular request. Returns the size of the tag message.
* May return 0 if TCQ is disabled for this device.
**/
static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char *msg)
{
struct request *req = cmd->request;
if (blk_rq_tagged(req)) {
*msg++ = MSG_SIMPLE_TAG;
*msg++ = req->tag;
return 2;
}
return 0;
}
static inline struct scsi_cmnd *scsi_mq_find_tag(struct Scsi_Host *shost,
unsigned int hw_ctx, int tag)
{
struct request *req;
req = blk_mq_tag_to_rq(shost->tag_set.tags[hw_ctx], tag);
return req ? (struct scsi_cmnd *)req->special : NULL;
}
/**
* scsi_find_tag - find a tagged command by device
* @SDpnt: pointer to the ScSI device
* @tag: the tag number
*
* Notes:
* Only works with tags allocated by the generic blk layer.
**/
static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev, int tag)
{
struct request *req;
if (tag != SCSI_NO_TAG) {
if (shost_use_blk_mq(sdev->host))
return scsi_mq_find_tag(sdev->host, 0, tag);
req = blk_queue_find_tag(sdev->request_queue, tag);
return req ? (struct scsi_cmnd *)req->special : NULL;
}
/* single command, look in space */
return sdev->current_cmnd;
}
/**
* scsi_init_shared_tag_map - create a shared tag map
* @shost: the host to share the tag map among all devices
* @depth: the total depth of the map
*/
static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
{
/*
* We always have a shared tag map around when using blk-mq.
*/
if (shost_use_blk_mq(shost))
return 0;
/*
* If the shared tag map isn't already initialized, do it now.
* This saves callers from having to check ->bqt when setting up
* devices on the shared host (for libata)
*/
if (!shost->bqt) {
shost->bqt = blk_init_tags(depth);
if (!shost->bqt)
return -ENOMEM;
}
return 0;
}
/**
* scsi_host_find_tag - find the tagged command by host
* @shost: pointer to scsi_host
* @tag: tag of the scsi_cmnd
*
* Notes:
* Only works with tags allocated by the generic blk layer.
**/
static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
int tag)
{
struct request *req;
if (tag != SCSI_NO_TAG) {
if (shost_use_blk_mq(shost))
return scsi_mq_find_tag(shost, 0, tag);
req = blk_map_queue_find_tag(shost->bqt, tag);
return req ? (struct scsi_cmnd *)req->special : NULL;
}
return NULL;
}
#endif /* CONFIG_BLOCK */
#endif /* _SCSI_SCSI_TCQ_H */