scsi: target: core: Fix backend plugging

target_core_iblock is plugging and unplugging on every command and this is
causing perf issues for drivers that prefer batched cmds. With recent
patches we can now take multiple cmds from a fabric driver queue and then
pass them down the backend drivers in a batch. This patch adds this support
by adding 2 callouts to the backend for plugging and unplugging the
device. Subsequent commits will add support for iblock and tcmu device
plugging.

Link: https://lore.kernel.org/r/20210227170006.5077-22-michael.christie@oracle.com
Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index eea7c27..1245c28 100644 (file)
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1807,10 +1807,42 @@ void target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
 }
 EXPORT_SYMBOL(target_submit_cmd);
 
+
+static struct se_dev_plug *target_plug_device(struct se_device *se_dev)
+{
+       struct se_dev_plug *se_plug;
+
+       if (!se_dev->transport->plug_device)
+               return NULL;
+
+       se_plug = se_dev->transport->plug_device(se_dev);
+       if (!se_plug)
+               return NULL;
+
+       se_plug->se_dev = se_dev;
+       /*
+        * We have a ref to the lun at this point, but the cmds could
+        * complete before we unplug, so grab a ref to the se_device so we
+        * can call back into the backend.
+        */
+       config_group_get(&se_dev->dev_group);
+       return se_plug;
+}
+
+static void target_unplug_device(struct se_dev_plug *se_plug)
+{
+       struct se_device *se_dev = se_plug->se_dev;
+
+       se_dev->transport->unplug_device(se_plug);
+       config_group_put(&se_dev->dev_group);
+}
+
 void target_queued_submit_work(struct work_struct *work)
 {
        struct se_cmd_queue *sq = container_of(work, struct se_cmd_queue, work);
        struct se_cmd *se_cmd, *next_cmd;
+       struct se_dev_plug *se_plug = NULL;
+       struct se_device *se_dev = NULL;
        struct llist_node *cmd_list;
 
        cmd_list = llist_del_all(&sq->cmd_list);
@@ -1819,8 +1851,17 @@ void target_queued_submit_work(struct work_struct *work)
                return;
 
        cmd_list = llist_reverse_order(cmd_list);
-       llist_for_each_entry_safe(se_cmd, next_cmd, cmd_list, se_cmd_list)
+       llist_for_each_entry_safe(se_cmd, next_cmd, cmd_list, se_cmd_list) {
+               if (!se_dev) {
+                       se_dev = se_cmd->se_dev;
+                       se_plug = target_plug_device(se_dev);
+               }
+
                target_submit(se_cmd);
+       }
+
+       if (se_plug)
+               target_unplug_device(se_plug);
 }
 
 /**

diff --git a/include/target/target_core_backend.h b/include/target/target_core_backend.h
index ce2fba4..1f78b09 100644 (file)
--- a/include/target/target_core_backend.h
+++ b/include/target/target_core_backend.h
@@ -34,6 +34,8 @@ struct target_backend_ops {
        int (*configure_device)(struct se_device *);
        void (*destroy_device)(struct se_device *);
        void (*free_device)(struct se_device *device);
+       struct se_dev_plug *(*plug_device)(struct se_device *se_dev);
+       void (*unplug_device)(struct se_dev_plug *se_plug);
 
        ssize_t (*set_configfs_dev_params)(struct se_device *,
                                           const char *, ssize_t);

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index fbe5b5b..cf445c3 100644 (file)
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -770,6 +770,10 @@ struct se_cmd_queue {
        struct work_struct      work;
 };
 
+struct se_dev_plug {
+       struct se_device        *se_dev;
+};
+
 struct se_device_queue {
        struct list_head        state_list;
        spinlock_t              lock;