[PATCH 17/17] vhost scsi: drop submission workqueue

[Mike Christie <michael.christie@oracle.com>]

We can't control a VM's vhost scsi IO right now because the vhost worker
is added to the VM's blk cgroup, but the vhost worker thread actually
just passes the cmd to a vhost-scsi driver workqueue which ends up
submitting the cmd to the block layer.

This patch has us submit from the vhost worker thread and removes the
work queue.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
---
 drivers/vhost/scsi.c | 30 +++---------------------------
 1 file changed, 3 insertions(+), 27 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 4e91a90..3178bf54 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -101,8 +101,6 @@ struct vhost_scsi_cmd {
 	struct vhost_scsi_nexus *tvc_nexus;
 	/* The TCM I/O descriptor that is accessed via container_of() */
 	struct se_cmd tvc_se_cmd;
-	/* work item used for cmwq dispatch to vhost_scsi_submission_work() */
-	struct work_struct work;
 	/* Copy of the incoming SCSI command descriptor block (CDB) */
 	unsigned char tvc_cdb[VHOST_SCSI_MAX_CDB_SIZE];
 	/* Sense buffer that will be mapped into outgoing status */
@@ -240,8 +238,6 @@ struct vhost_scsi_ctx {
 	struct iov_iter out_iter;
 };
 
-static struct workqueue_struct *vhost_scsi_workqueue;
-
 /* Global spinlock to protect vhost_scsi TPG list for vhost IOCTL access */
 static DEFINE_MUTEX(vhost_scsi_mutex);
 static LIST_HEAD(vhost_scsi_list);
@@ -776,10 +772,8 @@ static int vhost_scsi_to_tcm_attr(int attr)
 	return TCM_SIMPLE_TAG;
 }
 
-static void vhost_scsi_submission_work(struct work_struct *work)
+static void vhost_scsi_target_submit(struct vhost_scsi_cmd *cmd)
 {
-	struct vhost_scsi_cmd *cmd -		container_of(work, struct vhost_scsi_cmd, work);
 	struct vhost_scsi_nexus *tv_nexus;
 	struct se_cmd *se_cmd = &cmd->tvc_se_cmd;
 	struct scatterlist *sg_ptr, *sg_prot_ptr = NULL;
@@ -1126,14 +1120,7 @@ static u16 vhost_buf_to_lun(u8 *lun_buf)
 		 * vhost_scsi_queue_data_in() and vhost_scsi_queue_status()
 		 */
 		cmd->tvc_vq_desc = vc.head;
-		/*
-		 * Dispatch cmd descriptor for cmwq execution in process
-		 * context provided by vhost_scsi_workqueue.  This also ensures
-		 * cmd is executed on the same kworker CPU as this vhost
-		 * thread to gain positive L2 cache locality effects.
-		 */
-		INIT_WORK(&cmd->work, vhost_scsi_submission_work);
-		queue_work(vhost_scsi_workqueue, &cmd->work);
+		vhost_scsi_target_submit(cmd);
 		ret = 0;
 err:
 		/*
@@ -2511,17 +2498,9 @@ static int __init vhost_scsi_init(void)
 		" on "UTS_RELEASE"\n", VHOST_SCSI_VERSION, utsname()->sysname,
 		utsname()->machine);
 
-	/*
-	 * Use our own dedicated workqueue for submitting I/O into
-	 * target core to avoid contention within system_wq.
-	 */
-	vhost_scsi_workqueue = alloc_workqueue("vhost_scsi", 0, 0);
-	if (!vhost_scsi_workqueue)
-		goto out;
-
 	ret = vhost_scsi_register();
 	if (ret < 0)
-		goto out_destroy_workqueue;
+		goto out;
 
 	ret = target_register_template(&vhost_scsi_ops);
 	if (ret < 0)
@@ -2531,8 +2510,6 @@ static int __init vhost_scsi_init(void)
 
 out_vhost_scsi_deregister:
 	vhost_scsi_deregister();
-out_destroy_workqueue:
-	destroy_workqueue(vhost_scsi_workqueue);
 out:
 	return ret;
 };
@@ -2541,7 +2518,6 @@ static void vhost_scsi_exit(void)
 {
 	target_unregister_template(&vhost_scsi_ops);
 	vhost_scsi_deregister();
-	destroy_workqueue(vhost_scsi_workqueue);
 };
 
 MODULE_DESCRIPTION("VHOST_SCSI series fabric driver");
-- 
1.8.3.1