[PATCH 1/4] ufs: Avoid busy-waiting by eliminating tag conflicts

Bart Van Assche
2019-10-31T22:55:37Z

Instead of tracking which tags are in use in the ufs_hba.lrb_in_use
bitmask, rely on the block layer tag allocation mechanism. This patch
removes the following busy-waiting loop if ufshcd_issue_devman_upiu_cmd()
and the block layer accidentally allocate the same tag for a SCSI request:
* ufshcd_queuecommand() returns SCSI_MLQUEUE_HOST_BUSY.
* The SCSI core requeues the SCSI command.

Cc: Yaniv Gardi <ygardi@codeaurora.org>
Cc: Subhash Jadavani <subhashj@codeaurora.org>
Cc: Stanley Chu <stanley.chu@mediatek.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
drivers/scsi/ufs/ufshcd.c | 117 +++++++++++++++-----------------------
drivers/scsi/ufs/ufshcd.h | 9 +--
2 files changed, 50 insertions(+), 76 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 9fc05a535624..da9677fb2d5d 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -497,8 +497,8 @@ static void ufshcd_print_tmrs(struct ufs_hba *hba, unsigned long bitmap)
static void ufshcd_print_host_state(struct ufs_hba *hba)
{
dev_err(hba->dev, "UFS Host state=%d\n", hba->ufshcd_state);
- dev_err(hba->dev, "lrb in use=0x%lx, outstanding reqs=0x%lx tasks=0x%lx\n",
- hba->lrb_in_use, hba->outstanding_reqs, hba->outstanding_tasks);
+ dev_err(hba->dev, "outstanding reqs=0x%lx tasks=0x%lx\n",
+ hba->outstanding_reqs, hba->outstanding_tasks);
dev_err(hba->dev, "saved_err=0x%x, saved_uic_err=0x%x\n",
hba->saved_err, hba->saved_uic_err);
dev_err(hba->dev, "Device power mode=%d, UIC link state=%d\n",
@@ -1596,6 +1596,24 @@ int ufshcd_hold(struct ufs_hba *hba, bool async)
}
EXPORT_SYMBOL_GPL(ufshcd_hold);

+static bool ufshcd_is_busy(struct request *req, void *priv, bool reserved)
+{
+ int *busy = priv;
+
+ (*busy)++;
+ return false;
+}
+
+/* Whether or not any tag is in use by a request that is in progress. */
+static bool ufshcd_any_tag_in_use(struct ufs_hba *hba)
+{
+ struct request_queue *q = hba->tag_alloc_queue;
+ int busy = 0;
+
+ blk_mq_tagset_busy_iter(q->tag_set, ufshcd_is_busy, &busy);
+ return busy;
+}
+
static void ufshcd_gate_work(struct work_struct *work)
{
struct ufs_hba *hba = container_of(work, struct ufs_hba,
@@ -1619,7 +1637,7 @@ static void ufshcd_gate_work(struct work_struct *work)

if (hba->clk_gating.active_reqs
|| hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL
- || hba->lrb_in_use || hba->outstanding_tasks
+ || ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks
|| hba->active_uic_cmd || hba->uic_async_done)
goto rel_lock;

@@ -1673,7 +1691,7 @@ static void __ufshcd_release(struct ufs_hba *hba)

if (hba->clk_gating.active_reqs || hba->clk_gating.is_suspended
|| hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL
- || hba->lrb_in_use || hba->outstanding_tasks
+ || ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks
|| hba->active_uic_cmd || hba->uic_async_done
|| ufshcd_eh_in_progress(hba))
return;
@@ -2443,22 +2461,9 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)

hba->req_abort_count = 0;

- /* acquire the tag to make sure device cmds don't use it */
- if (test_and_set_bit_lock(tag, &hba->lrb_in_use)) {
- /*
- * Dev manage command in progress, requeue the command.
- * Requeuing the command helps in cases where the request *may*
- * find different tag instead of waiting for dev manage command
- * completion.
- */
- err = SCSI_MLQUEUE_HOST_BUSY;
- goto out;
- }
-
err = ufshcd_hold(hba, true);
if (err) {
err = SCSI_MLQUEUE_HOST_BUSY;
- clear_bit_unlock(tag, &hba->lrb_in_use);
goto out;
}
WARN_ON(hba->clk_gating.state != CLKS_ON);
@@ -2479,7 +2484,6 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
err = ufshcd_map_sg(hba, lrbp);
if (err) {
lrbp->cmd = NULL;
- clear_bit_unlock(tag, &hba->lrb_in_use);
goto out;
}
/* Make sure descriptors are ready before ringing the doorbell */
@@ -2625,44 +2629,6 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
return err;
}

-/**
- * ufshcd_get_dev_cmd_tag - Get device management command tag
- * @hba: per-adapter instance
- * @tag_out: pointer to variable with available slot value
- *
- * Get a free slot and lock it until device management command
- * completes.
- *
- * Returns false if free slot is unavailable for locking, else
- * return true with tag value in @tag.
- */
-static bool ufshcd_get_dev_cmd_tag(struct ufs_hba *hba, int *tag_out)
-{
- int tag;
- bool ret = false;
- unsigned long tmp;
-
- if (!tag_out)
- goto out;
-
- do {
- tmp = ~hba->lrb_in_use;
- tag = find_last_bit(&tmp, hba->nutrs);
- if (tag >= hba->nutrs)
- goto out;
- } while (test_and_set_bit_lock(tag, &hba->lrb_in_use));
-
- *tag_out = tag;
- ret = true;
-out:
- return ret;
-}
-
-static inline void ufshcd_put_dev_cmd_tag(struct ufs_hba *hba, int tag)
-{
- clear_bit_unlock(tag, &hba->lrb_in_use);
-}
-
/**
* ufshcd_exec_dev_cmd - API for sending device management requests
* @hba: UFS hba
@@ -2675,6 +2641,8 @@ static inline void ufshcd_put_dev_cmd_tag(struct ufs_hba *hba, int tag)
static int ufshcd_exec_dev_cmd(struct ufs_hba *hba,
enum dev_cmd_type cmd_type, int timeout)
{
+ struct request_queue *q = hba->tag_alloc_queue;
+ struct request *req;
struct ufshcd_lrb *lrbp;
int err;
int tag;
@@ -2688,7 +2656,10 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba *hba,
* Even though we use wait_event() which sleeps indefinitely,
* the maximum wait time is bounded by SCSI request timeout.
*/
- wait_event(hba->dev_cmd.tag_wq, ufshcd_get_dev_cmd_tag(hba, &tag));
+ req = blk_get_request(q, REQ_OP_DRV_IN, 0);
+ if (IS_ERR(req))
+ return PTR_ERR(req);
+ tag = req->tag;

init_completion(&wait);
lrbp = &hba->lrb[tag];
@@ -2712,8 +2683,7 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba *hba,
err ? "query_complete_err" : "query_complete");

out_put_tag:
- ufshcd_put_dev_cmd_tag(hba, tag);
- wake_up(&hba->dev_cmd.tag_wq);
+ blk_put_request(req);
up_read(&hba->clk_scaling_lock);
return err;
}
@@ -4832,7 +4802,6 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
cmd->result = result;
/* Mark completed command as NULL in LRB */
lrbp->cmd = NULL;
- clear_bit_unlock(index, &hba->lrb_in_use);
/* Do not touch lrbp after scsi done */
cmd->scsi_done(cmd);
__ufshcd_release(hba);
@@ -4854,9 +4823,6 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
hba->outstanding_reqs ^= completed_reqs;

ufshcd_clk_scaling_update_busy(hba);
-
- /* we might have free'd some tags above */
- wake_up(&hba->dev_cmd.tag_wq);
}

/**
@@ -5785,6 +5751,8 @@ static int ufshcd_issue_devman_upiu_cmd(struct ufs_hba *hba,
enum dev_cmd_type cmd_type,
enum query_opcode desc_op)
{
+ struct request_queue *q = hba->tag_alloc_queue;
+ struct request *req;
struct ufshcd_lrb *lrbp;
int err = 0;
int tag;
@@ -5794,7 +5762,10 @@ static int ufshcd_issue_devman_upiu_cmd(struct ufs_hba *hba,

down_read(&hba->clk_scaling_lock);

- wait_event(hba->dev_cmd.tag_wq, ufshcd_get_dev_cmd_tag(hba, &tag));
+ req = blk_get_request(q, REQ_OP_DRV_IN, 0);
+ if (IS_ERR(req))
+ return PTR_ERR(req);
+ tag = req->tag;

init_completion(&wait);
lrbp = &hba->lrb[tag];
@@ -5868,8 +5839,7 @@ static int ufshcd_issue_devman_upiu_cmd(struct ufs_hba *hba,
}
}

- ufshcd_put_dev_cmd_tag(hba, tag);
- wake_up(&hba->dev_cmd.tag_wq);
+ blk_put_request(req);
up_read(&hba->clk_scaling_lock);
return err;
}
@@ -6164,9 +6134,6 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
hba->lrb[tag].cmd = NULL;
spin_unlock_irqrestore(host->host_lock, flags);

- clear_bit_unlock(tag, &hba->lrb_in_use);
- wake_up(&hba->dev_cmd.tag_wq);
-
out:
if (!err) {
err = SUCCESS;
@@ -6873,6 +6840,11 @@ static int ufshcd_probe_hba(struct ufs_hba *hba)
int ret;
ktime_t start = ktime_get();

+ ret = -ENOMEM;
+ hba->tag_alloc_queue = blk_mq_init_queue(&hba->host->tag_set);
+ if (!hba->tag_alloc_queue)
+ goto out;
+
ret = ufshcd_link_startup(hba);
if (ret)
goto out;
@@ -7505,6 +7477,10 @@ static void ufshcd_hba_exit(struct ufs_hba *hba)
ufshcd_setup_hba_vreg(hba, false);
hba->is_powered = false;
}
+
+ if (hba->tag_alloc_queue)
+ blk_cleanup_queue(hba->tag_alloc_queue);
+ hba->tag_alloc_queue = NULL;
}

static int
@@ -8346,9 +8322,6 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)

init_rwsem(&hba->clk_scaling_lock);

- /* Initialize device management tag acquire wait queue */
- init_waitqueue_head(&hba->dev_cmd.tag_wq);
-
ufshcd_init_clk_gating(hba);

ufshcd_init_clk_scaling(hba);
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index e3593cce23c1..8fa33fb71237 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -212,13 +212,11 @@ struct ufs_query {
* @type: device management command type - Query, NOP OUT
* @lock: lock to allow one command at a time
* @complete: internal commands completion
- * @tag_wq: wait queue until free command slot is available
*/
struct ufs_dev_cmd {
enum dev_cmd_type type;
struct mutex lock;
struct completion *complete;
- wait_queue_head_t tag_wq;
struct ufs_query query;
};

@@ -480,7 +478,10 @@ struct ufs_stats {
* @host: Scsi_Host instance of the driver
* @dev: device handle
* @lrb: local reference block
- * @lrb_in_use: lrb in use
+ * @tag_alloc_queue: None of the exported block layer functions allows to
+ * allocate a tag directly from a tag set. The purpose of this request queue
+ * is to support allocating tags from hba->host->tag_set before any LUNs have
+ * been associated with this HBA.
* @outstanding_tasks: Bits representing outstanding task requests
* @outstanding_reqs: Bits representing outstanding transfer requests
* @capabilities: UFS Controller Capabilities
@@ -538,6 +539,7 @@ struct ufs_hba {

struct Scsi_Host *host;
struct device *dev;
+ struct request_queue *tag_alloc_queue;
/*
* This field is to keep a reference to "scsi_device" corresponding to
* "UFS device" W-LU.
@@ -558,7 +560,6 @@ struct ufs_hba {
u32 ahit;

struct ufshcd_lrb *lrb;
- unsigned long lrb_in_use;

unsigned long outstanding_tasks;
unsigned long outstanding_reqs;
--
2.24.0.rc0.303.g954a862665-goog