Re: [PATCH 13/14] scsi: add support for a blk-mq based I/O path.

From: Hannes Reinecke
Date: Wed Jul 09 2014 - 07:25:23 EST

On 06/25/2014 06:52 PM, Christoph Hellwig wrote:
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@xxxxxx>
---
drivers/scsi/hosts.c | 30 ++-
drivers/scsi/scsi.c | 5 +-
drivers/scsi/scsi_lib.c | 475 +++++++++++++++++++++++++++++++++++++++------
drivers/scsi/scsi_priv.h | 3 +
drivers/scsi/scsi_scan.c | 5 +-
drivers/scsi/scsi_sysfs.c | 2 +
include/scsi/scsi_host.h | 18 +-
include/scsi/scsi_tcq.h | 28 ++-
8 files changed, 494 insertions(+), 72 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 0632eee..6322e6c 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -213,9 +213,24 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
goto fail;
}

+ if (shost_use_blk_mq(shost)) {
+ error = scsi_mq_setup_tags(shost);
+ if (error)
+ goto fail;
+ }
+
+ /*
+ * Note that we allocate the freelist even for the MQ case for now,
+ * as we need a command set aside for scsi_reset_provider. Having
+ * the full host freelist and one command available for that is a
+ * little heavy-handed, but avoids introducing a special allocator
+ * just for this. Eventually the structure of scsi_reset_provider
+ * will need a major overhaul.
+ */
error = scsi_setup_command_freelist(shost);
if (error)
- goto fail;
+ goto out_destroy_tags;
+

if (!shost->shost_gendev.parent)
shost->shost_gendev.parent = dev ? dev : &platform_bus;
@@ -226,7 +241,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,

error = device_add(&shost->shost_gendev);
if (error)
- goto out;
+ goto out_destroy_freelist;

pm_runtime_set_active(&shost->shost_gendev);
pm_runtime_enable(&shost->shost_gendev);
@@ -279,8 +294,11 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
device_del(&shost->shost_dev);
out_del_gendev:
device_del(&shost->shost_gendev);
- out:
+ out_destroy_freelist:
scsi_destroy_command_freelist(shost);
+ out_destroy_tags:
+ if (shost_use_blk_mq(shost))
+ scsi_mq_destroy_tags(shost);
fail:
return error;
}
@@ -309,7 +327,9 @@ static void scsi_host_dev_release(struct device *dev)
}

scsi_destroy_command_freelist(shost);
- if (shost->bqt)
+ if (shost_use_blk_mq(shost) && shost->tag_set.tags)
+ scsi_mq_destroy_tags(shost);
+ else if (shost->bqt)
blk_free_tags(shost->bqt);

kfree(shost->shost_data);
@@ -436,6 +456,8 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
else
shost->dma_boundary = 0xffffffff;

+ shost->use_blk_mq = scsi_use_blk_mq && !shost->hostt->disable_blk_mq;
+
device_initialize(&shost->shost_gendev);
dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
shost->shost_gendev.bus = &scsi_bus_type;
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index b362058..c089812 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -809,7 +809,7 @@ void scsi_adjust_queue_depth(struct scsi_device *sdev, int tagged, int tags)
* is more IO than the LLD's can_queue (so there are not enuogh
* tags) request_fn's host queue ready check will handle it.
*/
- if (!sdev->host->bqt) {
+ if (!shost_use_blk_mq(sdev->host) && !sdev->host->bqt) {
if (blk_queue_tagged(sdev->request_queue) &&
blk_queue_resize_tags(sdev->request_queue, tags) != 0)
goto out;
@@ -1363,6 +1363,9 @@ MODULE_LICENSE("GPL");
module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

+bool scsi_use_blk_mq = false;
+module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);
+
static int __init init_scsi(void)
{
int error;
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 900b1c0..5d39cfc 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1,5 +1,6 @@
/*
- * scsi_lib.c Copyright (C) 1999 Eric Youngdale
+ * Copyright (C) 1999 Eric Youngdale
+ * Copyright (C) 2014 Christoph Hellwig
*
* SCSI queueing library.
* Initial versions: Eric Youngdale (eric@xxxxxxxxxxx).
@@ -20,6 +21,7 @@
#include <linux/delay.h>
#include <linux/hardirq.h>
#include <linux/scatterlist.h>
+#include <linux/blk-mq.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
@@ -113,6 +115,16 @@ scsi_set_blocked(struct scsi_cmnd *cmd, int reason)
}
}

+static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd)
+{
+ struct scsi_device *sdev = cmd->device;
+ struct request_queue *q = cmd->request->q;
+
+ blk_mq_requeue_request(cmd->request);
+ blk_mq_kick_requeue_list(q);
+ put_device(&sdev->sdev_gendev);
+}
+
/**
* __scsi_queue_insert - private queue insertion
* @cmd: The SCSI command being requeued
@@ -150,6 +162,10 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
* before blk_cleanup_queue() finishes.
*/
cmd->result = 0;
+ if (q->mq_ops) {
+ scsi_mq_requeue_cmd(cmd);
+ return;
+ }
spin_lock_irqsave(q->queue_lock, flags);
blk_requeue_request(q, cmd->request);
kblockd_schedule_work(&device->requeue_work);
@@ -308,6 +324,14 @@ void scsi_device_unbusy(struct scsi_device *sdev)
atomic_dec(&sdev->device_busy);
}

+static void scsi_kick_queue(struct request_queue *q)
+{
+ if (q->mq_ops)
+ blk_mq_start_hw_queues(q);
+ else
+ blk_run_queue(q);
+}
+
/*
* Called for single_lun devices on IO completion. Clear starget_sdev_user,
* and call blk_run_queue for all the scsi_devices on the target -
@@ -332,7 +356,7 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev)
* but in most cases, we will be first. Ideally, each LU on the
* target would get some limited time or requests on the target.
*/
- blk_run_queue(current_sdev->request_queue);
+ scsi_kick_queue(current_sdev->request_queue);

spin_lock_irqsave(shost->host_lock, flags);
if (starget->starget_sdev_user)
@@ -345,7 +369,7 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev)
continue;

spin_unlock_irqrestore(shost->host_lock, flags);
- blk_run_queue(sdev->request_queue);
+ scsi_kick_queue(sdev->request_queue);
spin_lock_irqsave(shost->host_lock, flags);

scsi_device_put(sdev);
@@ -438,7 +462,7 @@ static void scsi_starved_list_run(struct Scsi_Host *shost)
continue;
spin_unlock_irqrestore(shost->host_lock, flags);

- blk_run_queue(slq);
+ scsi_kick_queue(slq);
blk_put_queue(slq);

spin_lock_irqsave(shost->host_lock, flags);
@@ -469,7 +493,10 @@ static void scsi_run_queue(struct request_queue *q)
if (!list_empty(&sdev->host->starved_list))
scsi_starved_list_run(sdev->host);

- blk_run_queue(q);
+ if (q->mq_ops)
+ blk_mq_start_stopped_hw_queues(q, false);
+ else
+ blk_run_queue(q);
}

void scsi_requeue_run_queue(struct work_struct *work)
@@ -567,25 +594,72 @@ static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
return mempool_alloc(sgp->pool, gfp_mask);
}

-static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
+static void scsi_free_sgtable(struct scsi_data_buffer *sdb, bool mq)
{
- __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, false, scsi_sg_free);
+ if (mq && sdb->table.nents <= SCSI_MAX_SG_SEGMENTS)
+ return;
+ __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, mq, scsi_sg_free);
}

static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
- gfp_t gfp_mask)
+ gfp_t gfp_mask, bool mq)
{
+ struct scatterlist *first_chunk = NULL;
int ret;

BUG_ON(!nents);

+ if (mq) {
+ if (nents <= SCSI_MAX_SG_SEGMENTS) {
+ sdb->table.nents = nents;
+ sg_init_table(sdb->table.sgl, sdb->table.nents);
+ return 0;
+ }
+ first_chunk = sdb->table.sgl;
+ }
+
ret = __sg_alloc_table(&sdb->table, nents, SCSI_MAX_SG_SEGMENTS,
- NULL, gfp_mask, scsi_sg_alloc);
+ first_chunk, gfp_mask, scsi_sg_alloc);
if (unlikely(ret))
- scsi_free_sgtable(sdb);
+ scsi_free_sgtable(sdb, mq);
return ret;
}

+static void scsi_uninit_cmd(struct scsi_cmnd *cmd)
+{
+ if (cmd->request->cmd_type == REQ_TYPE_FS) {
+ struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
+
+ if (drv->uninit_command)
+ drv->uninit_command(cmd);
+ }
+}
+
+static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
+{
+ if (cmd->sdb.table.nents)
+ scsi_free_sgtable(&cmd->sdb, true);
+ if (cmd->request->next_rq && cmd->request->next_rq->special)
+ scsi_free_sgtable(cmd->request->next_rq->special, true);
+ if (scsi_prot_sg_count(cmd))
+ scsi_free_sgtable(cmd->prot_sdb, true);
+}
+
+static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
+{
+ struct scsi_device *sdev = cmd->device;
+ unsigned long flags;
+
+ BUG_ON(list_empty(&cmd->list));
+
+ scsi_mq_free_sgtables(cmd);
+ scsi_uninit_cmd(cmd);
+
+ spin_lock_irqsave(&sdev->list_lock, flags);
+ list_del_init(&cmd->list);
+ spin_unlock_irqrestore(&sdev->list_lock, flags);
+}
+
/*
* Function: scsi_release_buffers()
*
@@ -605,12 +679,12 @@ static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
void scsi_release_buffers(struct scsi_cmnd *cmd)
{
if (cmd->sdb.table.nents)
- scsi_free_sgtable(&cmd->sdb);
+ scsi_free_sgtable(&cmd->sdb, false);

memset(&cmd->sdb, 0, sizeof(cmd->sdb));

if (scsi_prot_sg_count(cmd))
- scsi_free_sgtable(cmd->prot_sdb);
+ scsi_free_sgtable(cmd->prot_sdb, false);
}
EXPORT_SYMBOL(scsi_release_buffers);

@@ -618,7 +692,7 @@ static void scsi_release_bidi_buffers(struct scsi_cmnd *cmd)
{
struct scsi_data_buffer *bidi_sdb = cmd->request->next_rq->special;

- scsi_free_sgtable(bidi_sdb);
+ scsi_free_sgtable(bidi_sdb, false);
kmem_cache_free(scsi_sdb_cache, bidi_sdb);
cmd->request->next_rq->special = NULL;
}
@@ -629,8 +703,6 @@ static bool scsi_end_request(struct request *req, int error,
struct scsi_cmnd *cmd = req->special;
struct scsi_device *sdev = cmd->device;
struct request_queue *q = sdev->request_queue;
- unsigned long flags;
-

if (blk_update_request(req, error, bytes))
return true;
@@ -643,14 +715,38 @@ static bool scsi_end_request(struct request *req, int error,
if (blk_queue_add_random(q))
add_disk_randomness(req->rq_disk);

- spin_lock_irqsave(q->queue_lock, flags);
- blk_finish_request(req, error);
- spin_unlock_irqrestore(q->queue_lock, flags);
+ if (req->mq_ctx) {
+ /*
+ * In the MQ case the command gets freed by __blk_mq_end_io,
+ * so we have to do all cleanup that depends on it earlier.
+ *
+ * We also can't kick the queues from irq context, so we
+ * will have to defer it to a workqueue.
+ */
+ scsi_mq_uninit_cmd(cmd);
+
+ __blk_mq_end_io(req, error);
+
+ if (scsi_target(sdev)->single_lun ||
+ !list_empty(&sdev->host->starved_list))
+ kblockd_schedule_work(&sdev->requeue_work);
+ else
+ blk_mq_start_stopped_hw_queues(q, true);
+
+ put_device(&sdev->sdev_gendev);
+ } else {
+ unsigned long flags;
+
+ spin_lock_irqsave(q->queue_lock, flags);
+ blk_finish_request(req, error);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+
+ if (bidi_bytes)
+ scsi_release_bidi_buffers(cmd);
+ scsi_release_buffers(cmd);
+ scsi_next_command(cmd);
+ }

- if (bidi_bytes)
- scsi_release_bidi_buffers(cmd);
- scsi_release_buffers(cmd);
- scsi_next_command(cmd);
return false;
}

@@ -981,8 +1077,14 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
/* Unprep the request and put it back at the head of the queue.
* A new command will be prepared and issued.
*/
- scsi_release_buffers(cmd);
- scsi_requeue_command(q, cmd);
+ if (q->mq_ops) {
+ cmd->request->cmd_flags &= ~REQ_DONTPREP;
+ scsi_mq_uninit_cmd(cmd);
+ scsi_mq_requeue_cmd(cmd);
+ } else {
+ scsi_release_buffers(cmd);
+ scsi_requeue_command(q, cmd);
+ }
break;
case ACTION_RETRY:
/* Retry the same command immediately */
@@ -1004,9 +1106,8 @@ static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
* If sg table allocation fails, requeue request later.
*/
if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
- gfp_mask))) {
+ gfp_mask, req->mq_ctx != NULL)))
return BLKPREP_DEFER;
- }

/*
* Next, walk the list, and fill in the addresses and sizes of
@@ -1034,21 +1135,27 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
{
struct scsi_device *sdev = cmd->device;
struct request *rq = cmd->request;
+ bool is_mq = (rq->mq_ctx != NULL);
+ int error;

- int error = scsi_init_sgtable(rq, &cmd->sdb, gfp_mask);
+ error = scsi_init_sgtable(rq, &cmd->sdb, gfp_mask);
if (error)
goto err_exit;

if (blk_bidi_rq(rq)) {
- struct scsi_data_buffer *bidi_sdb = kmem_cache_zalloc(
- scsi_sdb_cache, GFP_ATOMIC);
- if (!bidi_sdb) {
- error = BLKPREP_DEFER;
- goto err_exit;
+ if (!rq->q->mq_ops) {
+ struct scsi_data_buffer *bidi_sdb =
+ kmem_cache_zalloc(scsi_sdb_cache, GFP_ATOMIC);
+ if (!bidi_sdb) {
+ error = BLKPREP_DEFER;
+ goto err_exit;
+ }
+
+ rq->next_rq->special = bidi_sdb;
}

- rq->next_rq->special = bidi_sdb;
- error = scsi_init_sgtable(rq->next_rq, bidi_sdb, GFP_ATOMIC);
+ error = scsi_init_sgtable(rq->next_rq, rq->next_rq->special,
+ GFP_ATOMIC);
if (error)
goto err_exit;
}
@@ -1060,7 +1167,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
BUG_ON(prot_sdb == NULL);
ivecs = blk_rq_count_integrity_sg(rq->q, rq->bio);

- if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask)) {
+ if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask, is_mq)) {
error = BLKPREP_DEFER;
goto err_exit;
}
@@ -1074,13 +1181,16 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
cmd->prot_sdb->table.nents = count;
}

- return BLKPREP_OK ;
-
+ return BLKPREP_OK;
err_exit:
- scsi_release_buffers(cmd);
- cmd->request->special = NULL;
- scsi_put_command(cmd);
- put_device(&sdev->sdev_gendev);
+ if (is_mq) {
+ scsi_mq_free_sgtables(cmd);
+ } else {
+ scsi_release_buffers(cmd);
+ cmd->request->special = NULL;
+ scsi_put_command(cmd);
+ put_device(&sdev->sdev_gendev);
+ }
return error;
}
EXPORT_SYMBOL(scsi_init_io);
@@ -1295,13 +1405,7 @@ out:

static void scsi_unprep_fn(struct request_queue *q, struct request *req)
{
- if (req->cmd_type == REQ_TYPE_FS) {
- struct scsi_cmnd *cmd = req->special;
- struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
-
- if (drv->uninit_command)
- drv->uninit_command(cmd);
- }
+ scsi_uninit_cmd(req->special);
}

/*
@@ -1318,7 +1422,11 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
busy = atomic_inc_return(&sdev->device_busy) - 1;
if (busy == 0 && atomic_read(&sdev->device_blocked) > 0) {
if (atomic_dec_return(&sdev->device_blocked) > 0) {
- blk_delay_queue(q, SCSI_QUEUE_DELAY);
+ /*
+ * For the MQ case we take care of this in the caller.
+ */
+ if (!q->mq_ops)
+ blk_delay_queue(q, SCSI_QUEUE_DELAY);
goto out_dec;
}
SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
@@ -1688,6 +1796,188 @@ out_delay:
blk_delay_queue(q, SCSI_QUEUE_DELAY);
}

+static inline int prep_to_mq(int ret)
+{
+ switch (ret) {
+ case BLKPREP_OK:
+ return 0;
+ case BLKPREP_DEFER:
+ return BLK_MQ_RQ_QUEUE_BUSY;
+ default:
+ return BLK_MQ_RQ_QUEUE_ERROR;
+ }
+}
+
+static int scsi_mq_prep_fn(struct request *req)
+{
+ struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
+ struct scsi_device *sdev = req->q->queuedata;
+ struct Scsi_Host *shost = sdev->host;
+ unsigned char *sense_buf = cmd->sense_buffer;
+ struct scatterlist *sg;
+
+ memset(cmd, 0, sizeof(struct scsi_cmnd));
+
+ req->special = cmd;
+
+ cmd->request = req;
+ cmd->device = sdev;
+ cmd->sense_buffer = sense_buf;
+
+ cmd->tag = req->tag;
+
+ req->cmd = req->__cmd;
+ cmd->cmnd = req->cmd;
+ cmd->prot_op = SCSI_PROT_NORMAL;
+
+ INIT_LIST_HEAD(&cmd->list);
+ INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
+ cmd->jiffies_at_alloc = jiffies;
+
+ /*
+ * XXX: cmd_list lookups are only used by two drivers, try to get
+ * rid of this list in common code.
+ */
+ spin_lock_irq(&sdev->list_lock);
+ list_add_tail(&cmd->list, &sdev->cmd_list);
+ spin_unlock_irq(&sdev->list_lock);
+
+ sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt->cmd_size;
+ cmd->sdb.table.sgl = sg;
+
+ if (scsi_host_get_prot(shost)) {
+ cmd->prot_sdb = (void *)sg +
+ shost->sg_tablesize * sizeof(struct scatterlist);
+ memset(cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));
+
+ cmd->prot_sdb->table.sgl =
+ (struct scatterlist *)(cmd->prot_sdb + 1);
+ }
+
+ if (blk_bidi_rq(req)) {
+ struct request *next_rq = req->next_rq;
+ struct scsi_data_buffer *bidi_sdb = blk_mq_rq_to_pdu(next_rq);
+
+ memset(bidi_sdb, 0, sizeof(struct scsi_data_buffer));
+ bidi_sdb->table.sgl =
+ (struct scatterlist *)(bidi_sdb + 1);
+
+ next_rq->special = bidi_sdb;
+ }
+
+ switch (req->cmd_type) {
+ case REQ_TYPE_FS:
+ return scsi_cmd_to_driver(cmd)->init_command(cmd);
+ case REQ_TYPE_BLOCK_PC:
+ return scsi_setup_blk_pc_cmnd(cmd->device, req);
+ default:
+ return BLKPREP_KILL;
+ }
+}
+
+static void scsi_mq_done(struct scsi_cmnd *cmd)
+{
+ trace_scsi_dispatch_cmd_done(cmd);
+ blk_mq_complete_request(cmd->request);
+}
+
+static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
+{
+ struct request_queue *q = req->q;
+ struct scsi_device *sdev = q->queuedata;
+ struct Scsi_Host *shost = sdev->host;
+ struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
+ int ret;
+ int reason;
+
+ ret = prep_to_mq(scsi_prep_state_check(sdev, req));
+ if (ret)
+ goto out;
+
+ ret = BLK_MQ_RQ_QUEUE_BUSY;
+ if (!get_device(&sdev->sdev_gendev))
+ goto out;
+
+ if (!scsi_dev_queue_ready(q, sdev))
+ goto out_put_device;
+ if (!scsi_target_queue_ready(shost, sdev))
+ goto out_dec_device_busy;
+ if (!scsi_host_queue_ready(q, shost, sdev))
+ goto out_dec_target_busy;
+
+ if (!(req->cmd_flags & REQ_DONTPREP)) {
+ ret = prep_to_mq(scsi_mq_prep_fn(req));
+ if (ret)
+ goto out_dec_host_busy;
+ req->cmd_flags |= REQ_DONTPREP;
+ }
+
+ scsi_init_cmd_errh(cmd);
+ cmd->scsi_done = scsi_mq_done;
+
+ reason = scsi_dispatch_cmd(cmd);
+ if (reason) {
+ scsi_set_blocked(cmd, reason);
+ ret = BLK_MQ_RQ_QUEUE_BUSY;
+ goto out_dec_host_busy;
+ }
+
+ return BLK_MQ_RQ_QUEUE_OK;
+
+out_dec_host_busy:
+ cancel_delayed_work(&cmd->abort_work);
+ atomic_dec(&shost->host_busy);
+out_dec_target_busy:
+ if (scsi_target(sdev)->can_queue > 0)
+ atomic_dec(&scsi_target(sdev)->target_busy);
+out_dec_device_busy:
+ atomic_dec(&sdev->device_busy);
+out_put_device:
+ put_device(&sdev->sdev_gendev);
+out:
+ switch (ret) {
+ case BLK_MQ_RQ_QUEUE_BUSY:
+ blk_mq_stop_hw_queue(hctx);
+ if (atomic_read(&sdev->device_busy) == 0 &&
+ !scsi_device_blocked(sdev))
+ blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
+ break;
+ case BLK_MQ_RQ_QUEUE_ERROR:
+ /*
+ * Make sure to release all allocated ressources when
+ * we hit an error, as we will never see this command
+ * again.
+ */
+ if (req->cmd_flags & REQ_DONTPREP)
+ scsi_mq_uninit_cmd(cmd);
+ break;
+ default:
+ break;
+ }
+ return ret;
+}
+
+static int scsi_init_request(void *data, struct request *rq,
+ unsigned int hctx_idx, unsigned int request_idx,
+ unsigned int numa_node)
+{
+ struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
+
+ cmd->sense_buffer = kzalloc_node(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL,
+ numa_node);
+ if (!cmd->sense_buffer)
+ return -ENOMEM;
+ return 0;
+}
+
+static void scsi_exit_request(void *data, struct request *rq,
+ unsigned int hctx_idx, unsigned int request_idx)
+{
+ struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
+
+ kfree(cmd->sense_buffer);
+}
+
u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
{
struct device *host_dev;
@@ -1710,16 +2000,10 @@ u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
}
EXPORT_SYMBOL(scsi_calculate_bounce_limit);

-struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
- request_fn_proc *request_fn)
+static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
{
- struct request_queue *q;
struct device *dev = shost->dma_dev;

- q = blk_init_queue(request_fn, NULL);
- if (!q)
- return NULL;
-
/*
* this limit is imposed by hardware restrictions
*/
@@ -1750,7 +2034,17 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
* blk_queue_update_dma_alignment() later.
*/
blk_queue_dma_alignment(q, 0x03);
+}

+struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
+ request_fn_proc *request_fn)
+{
+ struct request_queue *q;
+
+ q = blk_init_queue(request_fn, NULL);
+ if (!q)
+ return NULL;
+ __scsi_init_queue(shost, q);
return q;
}
EXPORT_SYMBOL(__scsi_alloc_queue);
@@ -1771,6 +2065,55 @@ struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
return q;
}

+static struct blk_mq_ops scsi_mq_ops = {
+ .map_queue = blk_mq_map_queue,
+ .queue_rq = scsi_queue_rq,
+ .complete = scsi_softirq_done,
+ .timeout = scsi_times_out,
+ .init_request = scsi_init_request,
+ .exit_request = scsi_exit_request,
+};
+
+struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev)
+{
+ sdev->request_queue = blk_mq_init_queue(&sdev->host->tag_set);
+ if (IS_ERR(sdev->request_queue))
+ return NULL;
+
+ sdev->request_queue->queuedata = sdev;
+ __scsi_init_queue(sdev->host, sdev->request_queue);
+ return sdev->request_queue;
+}
+
+int scsi_mq_setup_tags(struct Scsi_Host *shost)
+{
+ unsigned int cmd_size, sgl_size, tbl_size;
+
+ tbl_size = shost->sg_tablesize;
+ if (tbl_size > SCSI_MAX_SG_SEGMENTS)
+ tbl_size = SCSI_MAX_SG_SEGMENTS;
+ sgl_size = tbl_size * sizeof(struct scatterlist);
+ cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
+ if (scsi_host_get_prot(shost))
+ cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;
+
+ memset(&shost->tag_set, 0, sizeof(shost->tag_set));
+ shost->tag_set.ops = &scsi_mq_ops;
+ shost->tag_set.nr_hw_queues = 1;
+ shost->tag_set.queue_depth = shost->can_queue;
+ shost->tag_set.cmd_size = cmd_size;
+ shost->tag_set.numa_node = NUMA_NO_NODE;
+ shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+ shost->tag_set.driver_data = shost;
+
+ return blk_mq_alloc_tag_set(&shost->tag_set);
+}
+
+void scsi_mq_destroy_tags(struct Scsi_Host *shost)
+{
+ blk_mq_free_tag_set(&shost->tag_set);
+}
+
/*
* Function: scsi_block_requests()
*
@@ -2516,9 +2859,13 @@ scsi_internal_device_block(struct scsi_device *sdev)
* block layer from calling the midlayer with this device's
* request queue.
*/
- spin_lock_irqsave(q->queue_lock, flags);
- blk_stop_queue(q);
- spin_unlock_irqrestore(q->queue_lock, flags);
+ if (q->mq_ops) {
+ blk_mq_stop_hw_queues(q);
+ } else {
+ spin_lock_irqsave(q->queue_lock, flags);
+ blk_stop_queue(q);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+ }

return 0;
}
@@ -2564,9 +2911,13 @@ scsi_internal_device_unblock(struct scsi_device *sdev,
sdev->sdev_state != SDEV_OFFLINE)
return -EINVAL;

- spin_lock_irqsave(q->queue_lock, flags);
- blk_start_queue(q);
- spin_unlock_irqrestore(q->queue_lock, flags);
+ if (q->mq_ops) {
+ blk_mq_start_stopped_hw_queues(q, false);
+ } else {
+ spin_lock_irqsave(q->queue_lock, flags);
+ blk_start_queue(q);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+ }

return 0;
}
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index a45d1c2..12b8e1b 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;
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 4a6e4ba..b91cfaf 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -273,7 +273,10 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
*/
sdev->borken = 1;

- sdev->request_queue = scsi_alloc_queue(sdev);
+ if (shost_use_blk_mq(shost))
+ sdev->request_queue = scsi_mq_alloc_queue(sdev);
+ else
+ sdev->request_queue = scsi_alloc_queue(sdev);
if (!sdev->request_queue) {
/* release fn is set up in scsi_sysfs_device_initialise, so
* have to free and put manually here */
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index deef063..6c9227f 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -333,6 +333,7 @@ store_shost_eh_deadline(struct device *dev, struct device_attribute *attr,

static DEVICE_ATTR(eh_deadline, S_IRUGO | S_IWUSR, show_shost_eh_deadline, store_shost_eh_deadline);

+shost_rd_attr(use_blk_mq, "%d\n");
shost_rd_attr(unique_id, "%u\n");
shost_rd_attr(cmd_per_lun, "%hd\n");
shost_rd_attr(can_queue, "%hd\n");
@@ -352,6 +353,7 @@ show_host_busy(struct device *dev, struct device_attribute *attr, char *buf)
static DEVICE_ATTR(host_busy, S_IRUGO, show_host_busy, NULL);

static struct attribute *scsi_sysfs_shost_attrs[] = {
+ &dev_attr_use_blk_mq.attr,
&dev_attr_unique_id.attr,
&dev_attr_host_busy.attr,
&dev_attr_cmd_per_lun.attr,
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 7f9bbda..b54511e 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -7,6 +7,7 @@
#include <linux/workqueue.h>
#include <linux/mutex.h>
#include <linux/seq_file.h>
+#include <linux/blk-mq.h>
#include <scsi/scsi.h>

struct request_queue;
@@ -531,6 +532,9 @@ struct scsi_host_template {
*/
unsigned int cmd_size;
struct scsi_host_cmd_pool *cmd_pool;
+
+ /* temporary flag to disable blk-mq I/O path */
+ bool disable_blk_mq;
};

/*
@@ -601,7 +605,10 @@ struct Scsi_Host {
* Area to keep a shared tag map (if needed, will be
* NULL if not).
*/
- struct blk_queue_tag *bqt;
+ union {
+ struct blk_queue_tag *bqt;
+ struct blk_mq_tag_set tag_set;
+ };

atomic_t host_busy; /* commands actually active on low-level */
atomic_t host_blocked;
@@ -693,6 +700,8 @@ struct Scsi_Host {
/* The controller does not support WRITE SAME */
unsigned no_write_same:1;

+ unsigned use_blk_mq:1;
+
/*
* Optional work queue to be utilized by the transport
*/
@@ -793,6 +802,13 @@ static inline int scsi_host_in_recovery(struct Scsi_Host *shost)
shost->tmf_in_progress;
}

+extern bool scsi_use_blk_mq;
+
+static inline bool shost_use_blk_mq(struct Scsi_Host *shost)
+{
+ return shost->use_blk_mq;
+}
+
extern int scsi_queue_work(struct Scsi_Host *, struct work_struct *);
extern void scsi_flush_work(struct Scsi_Host *);

diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index 81dd12e..cdcc90b 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;
}

Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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