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authorChristoph Hellwig <hch@lst.de>2014-01-17 12:06:53 +0100
committerChristoph Hellwig <hch@lst.de>2014-07-25 17:16:28 -0400
commitd285203cf647d7c97db3a1c33794315c9008593f (patch)
treea28a0a902cf3f467e326a02f5632b917b75c56a3 /include/scsi/scsi_tcq.h
parentc53c6d6a68b13b1dff2892551b56cfdc07887d9e (diff)
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 'include/scsi/scsi_tcq.h')
-rw-r--r--include/scsi/scsi_tcq.h28
1 files changed, 25 insertions, 3 deletions
diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index 81dd12edc38c..cdcc90b07ecb 100644
--- a/include/scsi/scsi_tcq.h
+++ b/include/scsi/scsi_tcq.h
@@ -67,7 +67,8 @@ static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
if (!sdev->tagged_supported)
return;
- if (!blk_queue_tagged(sdev->request_queue))
+ if (!shost_use_blk_mq(sdev->host) &&
+ blk_queue_tagged(sdev->request_queue))
blk_queue_init_tags(sdev->request_queue, depth,
sdev->host->bqt);
@@ -80,7 +81,8 @@ static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
**/
static inline void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)
{
- if (blk_queue_tagged(sdev->request_queue))
+ 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);
}
@@ -108,6 +110,15 @@ static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char *msg)
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
@@ -118,10 +129,12 @@ static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char *msg)
**/
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;
}
@@ -130,6 +143,7 @@ static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev, int tag)
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
@@ -138,6 +152,12 @@ static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev, int tag)
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)
@@ -165,6 +185,8 @@ static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
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;
}