scsi: lpfc: Update lpfc_ramp_down_queue_handler() logic

Typically when an out of resource CQE status is detected, the
lpfc_ramp_down_queue_handler() logic is called to help reduce I/O load by
reducing an sdev's queue_depth.

However, the current lpfc_rampdown_queue_depth() logic does not help reduce
queue_depth.  num_cmd_success is never updated and is always zero, which
means new_queue_depth will always be set to sdev->queue_depth.  So,
new_queue_depth = sdev->queue_depth - new_queue_depth always sets
new_queue_depth to zero.  And, scsi_change_queue_depth(sdev, 0) is
essentially a no-op.

Change the lpfc_ramp_down_queue_handler() logic to set new_queue_depth
equal to sdev->queue_depth subtracted from number of times num_rsrc_err was
incremented.  If num_rsrc_err is >= sdev->queue_depth, then set
new_queue_depth equal to 1.  Eventually, the frequency of Good_Status
frames will signal SCSI upper layer to auto increase the queue_depth back
to the driver default of 64 via scsi_handle_queue_ramp_up().

Signed-off-by: Justin Tee <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Justin Tee

drivers/scsi/lpfc/lpfc.h

@@ -1333,7 +1333,6 @@ struct lpfc_hba {
 	struct timer_list fabric_block_timer;
 	unsigned long bit_flags;
 	atomic_t num_rsrc_err;
-	atomic_t num_cmd_success;
 	unsigned long last_rsrc_error_time;
 	unsigned long last_ramp_down_time;
 #ifdef CONFIG_SCSI_LPFC_DEBUG_FS

drivers/scsi/lpfc/lpfc_scsi.c

@@ -167,11 +167,10 @@ lpfc_ramp_down_queue_handler(struct lpfc_hba *phba)
 	struct Scsi_Host  *shost;
 	struct scsi_device *sdev;
 	unsigned long new_queue_depth;
-	unsigned long num_rsrc_err, num_cmd_success;
+	unsigned long num_rsrc_err;
 	int i;
 
 	num_rsrc_err = atomic_read(&phba->num_rsrc_err);
-	num_cmd_success = atomic_read(&phba->num_cmd_success);
 
 	/*
 	 * The error and success command counters are global per
@@ -186,20 +185,16 @@ lpfc_ramp_down_queue_handler(struct lpfc_hba *phba)
 		for (i = 0; i <= phba->max_vports && vports[i] != NULL; i++) {
 			shost = lpfc_shost_from_vport(vports[i]);
 			shost_for_each_device(sdev, shost) {
-				new_queue_depth =
-					sdev->queue_depth * num_rsrc_err /
-					(num_rsrc_err + num_cmd_success);
-				if (!new_queue_depth)
-					new_queue_depth = sdev->queue_depth - 1;
+				if (num_rsrc_err >= sdev->queue_depth)
+					new_queue_depth = 1;
 				else
 					new_queue_depth = sdev->queue_depth -
-								new_queue_depth;
+						num_rsrc_err;
 				scsi_change_queue_depth(sdev, new_queue_depth);
 			}
 		}
 	lpfc_destroy_vport_work_array(phba, vports);
 	atomic_set(&phba->num_rsrc_err, 0);
-	atomic_set(&phba->num_cmd_success, 0);
 }
 
 /**