scsi: ufs: Optimize the command queueing code

Remove the clock scaling lock from ufshcd_queuecommand() since it is a
performance bottleneck. Instead check the SCSI device budget bitmaps in the
code that waits for ongoing ufshcd_queuecommand() calls. A bit is set in
sdev->budget_map just before scsi_queue_rq() is called and a bit is cleared
from that bitmap if scsi_queue_rq() does not submit the request or after
the request has finished. See also the blk_mq_{get,put}_dispatch_budget()
calls in the block layer.

There is no risk for a livelock since the block layer delays queue reruns
if queueing a request fails because the SCSI host has been blocked.

Link: https://lore.kernel.org/r/20211203231950.193369-17-bvanassche@acm.org
Cc: Asutosh Das (asd) <asutoshd@codeaurora.org>
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 9f0a1f6..650dddf 100644 (file)
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1070,13 +1070,31 @@ static bool ufshcd_is_devfreq_scaling_required(struct ufs_hba *hba,
        return false;
 }
 
+/*
+ * Determine the number of pending commands by counting the bits in the SCSI
+ * device budget maps. This approach has been selected because a bit is set in
+ * the budget map before scsi_host_queue_ready() checks the host_self_blocked
+ * flag. The host_self_blocked flag can be modified by calling
+ * scsi_block_requests() or scsi_unblock_requests().
+ */
+static u32 ufshcd_pending_cmds(struct ufs_hba *hba)
+{
+       struct scsi_device *sdev;
+       u32 pending = 0;
+
+       shost_for_each_device(sdev, hba->host)
+               pending += sbitmap_weight(&sdev->budget_map);
+
+       return pending;
+}
+
 static int ufshcd_wait_for_doorbell_clr(struct ufs_hba *hba,
                                        u64 wait_timeout_us)
 {
        unsigned long flags;
        int ret = 0;
        u32 tm_doorbell;
-       u32 tr_doorbell;
+       u32 tr_pending;
        bool timeout = false, do_last_check = false;
        ktime_t start;
 
@@ -1094,8 +1112,8 @@ static int ufshcd_wait_for_doorbell_clr(struct ufs_hba *hba,
                }
 
                tm_doorbell = ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL);
-               tr_doorbell = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
-               if (!tm_doorbell && !tr_doorbell) {
+               tr_pending = ufshcd_pending_cmds(hba);
+               if (!tm_doorbell && !tr_pending) {
                        timeout = false;
                        break;
                } else if (do_last_check) {
@@ -1115,12 +1133,12 @@ static int ufshcd_wait_for_doorbell_clr(struct ufs_hba *hba,
                        do_last_check = true;
                }
                spin_lock_irqsave(hba->host->host_lock, flags);
-       } while (tm_doorbell || tr_doorbell);
+       } while (tm_doorbell || tr_pending);
 
        if (timeout) {
                dev_err(hba->dev,
                        "%s: timedout waiting for doorbell to clear (tm=0x%x, tr=0x%x)\n",
-                       __func__, tm_doorbell, tr_doorbell);
+                       __func__, tm_doorbell, tr_pending);
                ret = -EBUSY;
        }
 out:
@@ -2681,9 +2699,6 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 
        WARN_ONCE(tag < 0, "Invalid tag %d\n", tag);
 
-       if (!down_read_trylock(&hba->clk_scaling_lock))
-               return SCSI_MLQUEUE_HOST_BUSY;
-
        /*
         * Allows the UFS error handler to wait for prior ufshcd_queuecommand()
         * calls.
@@ -2772,8 +2787,6 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 out:
        rcu_read_unlock();
 
-       up_read(&hba->clk_scaling_lock);
-
        if (ufs_trigger_eh()) {
                unsigned long flags;
 

diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 8e94276..88c20f3 100644 (file)
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -778,6 +778,7 @@ struct ufs_hba_monitor {
  * @clk_list_head: UFS host controller clocks list node head
  * @pwr_info: holds current power mode
  * @max_pwr_info: keeps the device max valid pwm
+ * @clk_scaling_lock: used to serialize device commands and clock scaling
  * @desc_size: descriptor sizes reported by device
  * @urgent_bkops_lvl: keeps track of urgent bkops level for device
  * @is_urgent_bkops_lvl_checked: keeps track if the urgent bkops level for