scsi: target: tcmu: Add backend plug/unplug callouts

This patch adds plug/unplug callouts for tcmu, so we can avoid the number
of times we switch to userspace. Using this driver with tcm_loop is a
common config, and dependng on the nr_hw_queues (nr_hw_queues=1 performs
much better) and fio jobs (lower num jobs around 4) this patch can increase
IOPS by only around 5-10% because we hit other issues like the big per tcmu
device mutex.

Link: https://lore.kernel.org/r/20210227170006.5077-24-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_user.c b/drivers/target/target_core_user.c
index bf73cd5..48ccdf7 100644 (file)
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -111,6 +111,7 @@ struct tcmu_dev {
        struct kref kref;
 
        struct se_device se_dev;
+       struct se_dev_plug se_plug;
 
        char *name;
        struct se_hba *hba;
@@ -119,6 +120,7 @@ struct tcmu_dev {
 #define TCMU_DEV_BIT_BROKEN 1
 #define TCMU_DEV_BIT_BLOCKED 2
 #define TCMU_DEV_BIT_TMR_NOTIFY 3
+#define TCM_DEV_BIT_PLUGGED 4
        unsigned long flags;
 
        struct uio_info uio_info;
@@ -959,6 +961,25 @@ static uint32_t ring_insert_padding(struct tcmu_dev *udev, size_t cmd_size)
        return cmd_head;
 }
 
+static void tcmu_unplug_device(struct se_dev_plug *se_plug)
+{
+       struct se_device *se_dev = se_plug->se_dev;
+       struct tcmu_dev *udev = TCMU_DEV(se_dev);
+
+       clear_bit(TCM_DEV_BIT_PLUGGED, &udev->flags);
+       uio_event_notify(&udev->uio_info);
+}
+
+static struct se_dev_plug *tcmu_plug_device(struct se_device *se_dev)
+{
+       struct tcmu_dev *udev = TCMU_DEV(se_dev);
+
+       if (!test_and_set_bit(TCM_DEV_BIT_PLUGGED, &udev->flags))
+               return &udev->se_plug;
+
+       return NULL;
+}
+
 /**
  * queue_cmd_ring - queue cmd to ring or internally
  * @tcmu_cmd: cmd to queue
@@ -1086,8 +1107,8 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 
        list_add_tail(&tcmu_cmd->queue_entry, &udev->inflight_queue);
 
-       /* TODO: only if FLUSH and FUA? */
-       uio_event_notify(&udev->uio_info);
+       if (!test_bit(TCM_DEV_BIT_PLUGGED, &udev->flags))
+               uio_event_notify(&udev->uio_info);
 
        return 0;
 
@@ -2863,6 +2884,8 @@ static struct target_backend_ops tcmu_ops = {
        .configure_device       = tcmu_configure_device,
        .destroy_device         = tcmu_destroy_device,
        .free_device            = tcmu_free_device,
+       .unplug_device          = tcmu_unplug_device,
+       .plug_device            = tcmu_plug_device,
        .parse_cdb              = tcmu_parse_cdb,
        .tmr_notify             = tcmu_tmr_notify,
        .set_configfs_dev_params = tcmu_set_configfs_dev_params,