d285203cf6
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>
198 lines
4.7 KiB
C
198 lines
4.7 KiB
C
#ifndef _SCSI_SCSI_TCQ_H
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#define _SCSI_SCSI_TCQ_H
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#include <linux/blkdev.h>
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#include <scsi/scsi_cmnd.h>
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#include <scsi/scsi_device.h>
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#include <scsi/scsi_host.h>
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#define MSG_SIMPLE_TAG 0x20
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#define MSG_HEAD_TAG 0x21
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#define MSG_ORDERED_TAG 0x22
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#define MSG_ACA_TAG 0x24 /* unsupported */
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#define SCSI_NO_TAG (-1) /* identify no tag in use */
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#ifdef CONFIG_BLOCK
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/**
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* scsi_get_tag_type - get the type of tag the device supports
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* @sdev: the scsi device
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*
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* Notes:
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* If the drive only supports simple tags, returns MSG_SIMPLE_TAG
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* if it supports all tag types, returns MSG_ORDERED_TAG.
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*/
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static inline int scsi_get_tag_type(struct scsi_device *sdev)
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{
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if (!sdev->tagged_supported)
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return 0;
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if (sdev->ordered_tags)
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return MSG_ORDERED_TAG;
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if (sdev->simple_tags)
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return MSG_SIMPLE_TAG;
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return 0;
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}
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static inline void scsi_set_tag_type(struct scsi_device *sdev, int tag)
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{
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switch (tag) {
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case MSG_ORDERED_TAG:
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sdev->ordered_tags = 1;
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/* fall through */
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case MSG_SIMPLE_TAG:
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sdev->simple_tags = 1;
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break;
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case 0:
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/* fall through */
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default:
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sdev->ordered_tags = 0;
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sdev->simple_tags = 0;
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break;
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}
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}
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/**
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* scsi_activate_tcq - turn on tag command queueing
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* @SDpnt: device to turn on TCQ for
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* @depth: queue depth
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*
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* Notes:
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* Eventually, I hope depth would be the maximum depth
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* the device could cope with and the real queue depth
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* would be adjustable from 0 to depth.
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**/
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static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
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{
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if (!sdev->tagged_supported)
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return;
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if (!shost_use_blk_mq(sdev->host) &&
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blk_queue_tagged(sdev->request_queue))
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blk_queue_init_tags(sdev->request_queue, depth,
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sdev->host->bqt);
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scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
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}
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/**
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* scsi_deactivate_tcq - turn off tag command queueing
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* @SDpnt: device to turn off TCQ for
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**/
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static inline void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)
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{
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if (!shost_use_blk_mq(sdev->host) &&
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blk_queue_tagged(sdev->request_queue))
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blk_queue_free_tags(sdev->request_queue);
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scsi_adjust_queue_depth(sdev, 0, depth);
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}
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/**
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* scsi_populate_tag_msg - place a tag message in a buffer
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* @SCpnt: pointer to the Scsi_Cmnd for the tag
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* @msg: pointer to the area to place the tag
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*
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* Notes:
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* designed to create the correct type of tag message for the
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* particular request. Returns the size of the tag message.
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* May return 0 if TCQ is disabled for this device.
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**/
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static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char *msg)
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{
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struct request *req = cmd->request;
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if (blk_rq_tagged(req)) {
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*msg++ = MSG_SIMPLE_TAG;
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*msg++ = req->tag;
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return 2;
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}
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return 0;
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}
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static inline struct scsi_cmnd *scsi_mq_find_tag(struct Scsi_Host *shost,
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unsigned int hw_ctx, int tag)
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{
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struct request *req;
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req = blk_mq_tag_to_rq(shost->tag_set.tags[hw_ctx], tag);
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return req ? (struct scsi_cmnd *)req->special : NULL;
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}
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/**
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* scsi_find_tag - find a tagged command by device
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* @SDpnt: pointer to the ScSI device
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* @tag: the tag number
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*
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* Notes:
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* Only works with tags allocated by the generic blk layer.
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**/
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static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev, int tag)
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{
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struct request *req;
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if (tag != SCSI_NO_TAG) {
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if (shost_use_blk_mq(sdev->host))
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return scsi_mq_find_tag(sdev->host, 0, tag);
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req = blk_queue_find_tag(sdev->request_queue, tag);
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return req ? (struct scsi_cmnd *)req->special : NULL;
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}
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/* single command, look in space */
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return sdev->current_cmnd;
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}
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/**
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* scsi_init_shared_tag_map - create a shared tag map
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* @shost: the host to share the tag map among all devices
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* @depth: the total depth of the map
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*/
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static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
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{
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/*
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* We always have a shared tag map around when using blk-mq.
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*/
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if (shost_use_blk_mq(shost))
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return 0;
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/*
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* If the shared tag map isn't already initialized, do it now.
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* This saves callers from having to check ->bqt when setting up
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* devices on the shared host (for libata)
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*/
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if (!shost->bqt) {
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shost->bqt = blk_init_tags(depth);
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if (!shost->bqt)
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return -ENOMEM;
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}
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return 0;
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}
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/**
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* scsi_host_find_tag - find the tagged command by host
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* @shost: pointer to scsi_host
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* @tag: tag of the scsi_cmnd
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*
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* Notes:
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* Only works with tags allocated by the generic blk layer.
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**/
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static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
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int tag)
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{
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struct request *req;
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if (tag != SCSI_NO_TAG) {
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if (shost_use_blk_mq(shost))
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return scsi_mq_find_tag(shost, 0, tag);
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req = blk_map_queue_find_tag(shost->bqt, tag);
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return req ? (struct scsi_cmnd *)req->special : NULL;
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}
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return NULL;
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}
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#endif /* CONFIG_BLOCK */
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#endif /* _SCSI_SCSI_TCQ_H */
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