scsi: add use_cmd_list flag

Add a use_cmd_list flag in struct Scsi_Host to request keeping track of
all outstanding commands per device.

Default behaviour is not to keep track of cmd_list per sdev, as this may
introduce lock contention. (overhead is more on multi-node NUMA.), and
only enable it on the two drivers that need it.

Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

4 files changed, 15 insertions, 12 deletions

diff --git a/drivers/scsi/aacraid/linit.c b/drivers/scsi/aacraid/linit.c
index 63f576c9300a..a759cb2d4b15 100644
--- a/drivers/scsi/aacraid/linit.c
+++ b/drivers/scsi/aacraid/linit.c
@@ -1152,6 +1152,7 @@ static int aac_probe_one(struct pci_dev *pdev, const struct pci_device_id *id)
         shost->irq = pdev->irq;
         shost->unique_id = unique_id;
         shost->max_cmd_len = 16;
+        shost->use_cmd_list = 1;
 
         aac = (struct aac_dev *)shost->hostdata;
         aac->base_start = pci_resource_start(pdev, 0);
diff --git a/drivers/scsi/dpt_i2o.c b/drivers/scsi/dpt_i2o.c
index 67283ef418ac..072f0ec2851e 100644
--- a/drivers/scsi/dpt_i2o.c
+++ b/drivers/scsi/dpt_i2o.c
@@ -2363,6 +2363,7 @@ static s32 adpt_scsi_host_alloc(adpt_hba* pHba, struct scsi_host_template *sht)
         host->unique_id = (u32)sys_tbl_pa + pHba->unit;
         host->sg_tablesize = pHba->sg_tablesize;
         host->can_queue = pHba->post_fifo_size;
+        host->use_cmd_list = 1;
 
         return 0;
 }
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d837dc180522..b9a8ddd77eef 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -645,16 +645,18 @@ static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
 static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
 {
         struct scsi_device *sdev = cmd->device;
+        struct Scsi_Host *shost = sdev->host;
         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);
+        if (shost->use_cmd_list) {
+                BUG_ON(list_empty(&cmd->list));
+                spin_lock_irqsave(&sdev->list_lock, flags);
+                list_del_init(&cmd->list);
+                spin_unlock_irqrestore(&sdev->list_lock, flags);
+        }
 }
 
 /*
@@ -1815,13 +1817,11 @@ static int scsi_mq_prep_fn(struct request *req)
         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);
+        if (shost->use_cmd_list) {
+                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;
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index ba2034779961..cafb260ef2d3 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -680,6 +680,7 @@ struct Scsi_Host {
         unsigned no_write_same:1;
 
         unsigned use_blk_mq:1;
+        unsigned use_cmd_list:1;
 
         /*
          * Optional work queue to be utilized by the transport