[PATCH] scsi:tcmu: switch tcmu completion path to work queue context

Guixin Liu
2022-05-10T06:51:49Z

Currently, tcmu do completion in uio_write context, the userspace
will wait until tcmu`s done synchronously, switch completion path to
work queue context for better performance.

Use tcmu + file to evaluate performance,
fio job: fio -filename=/dev/sdb -direct=1 -size=2G -name=1 -thread
-runtime=60 -time_based -rw=randwrite -numjobs=16 -iodepth=16 -bs=128k

Without this patch:
READ: bw=2775MiB/s (2910MB/s), 173MiB/s-174MiB/s
(181MB/s-183MB/s), io=163GiB (175GB), run=60001-60001msec

With this patch:
READ: bw=3333MiB/s (3495MB/s), 208MiB/s-209MiB/s
(218MB/s-219MB/s), io=195GiB (210GB), run=60001-60001msec

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
drivers/target/target_core_user.c | 151 +++++++++++++++++++++-----------------
1 file changed, 84 insertions(+), 67 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index fd7267b..0eb3396 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -168,6 +168,8 @@ struct tcmu_dev {
char dev_config[TCMU_CONFIG_LEN];

int nl_reply_supported;
+
+ struct work_struct complete_work;
};

#define TCMU_DEV(_se_dev) container_of(_se_dev, struct tcmu_dev, se_dev)
@@ -223,6 +225,7 @@ struct tcmu_tmr {

static atomic_t global_page_count = ATOMIC_INIT(0);
static struct delayed_work tcmu_unmap_work;
+struct workqueue_struct *tcmu_comp_wq;
static int tcmu_global_max_pages = TCMU_GLOBAL_MAX_PAGES_DEF;

static int tcmu_set_global_max_data_area(const char *str,
@@ -1596,6 +1599,76 @@ static void tcmu_detach_hba(struct se_hba *hba)
hba->hba_ptr = NULL;
}

+static void run_qfull_queue(struct tcmu_dev *udev, bool fail)
+{
+ struct tcmu_cmd *tcmu_cmd, *tmp_cmd;
+ LIST_HEAD(cmds);
+ sense_reason_t scsi_ret;
+ int ret;
+
+ if (list_empty(&udev->qfull_queue))
+ return;
+
+ pr_debug("running %s's cmdr queue forcefail %d\n", udev->name, fail);
+
+ list_splice_init(&udev->qfull_queue, &cmds);
+
+ list_for_each_entry_safe(tcmu_cmd, tmp_cmd, &cmds, queue_entry) {
+ list_del_init(&tcmu_cmd->queue_entry);
+
+ pr_debug("removing cmd %p on dev %s from queue\n",
+ tcmu_cmd, udev->name);
+
+ if (fail) {
+ /*
+ * We were not able to even start the command, so
+ * fail with busy to allow a retry in case runner
+ * was only temporarily down. If the device is being
+ * removed then LIO core will do the right thing and
+ * fail the retry.
+ */
+ tcmu_cmd->se_cmd->priv = NULL;
+ target_complete_cmd(tcmu_cmd->se_cmd, SAM_STAT_BUSY);
+ tcmu_free_cmd(tcmu_cmd);
+ continue;
+ }
+
+ ret = queue_cmd_ring(tcmu_cmd, &scsi_ret);
+ if (ret < 0) {
+ pr_debug("cmd %p on dev %s failed with %u\n",
+ tcmu_cmd, udev->name, scsi_ret);
+ /*
+ * Ignore scsi_ret for now. target_complete_cmd
+ * drops it.
+ */
+ tcmu_cmd->se_cmd->priv = NULL;
+ target_complete_cmd(tcmu_cmd->se_cmd,
+ SAM_STAT_CHECK_CONDITION);
+ tcmu_free_cmd(tcmu_cmd);
+ } else if (ret > 0) {
+ pr_debug("ran out of space during cmdr queue run\n");
+ /*
+ * cmd was requeued, so just put all cmds back in
+ * the queue
+ */
+ list_splice_tail(&cmds, &udev->qfull_queue);
+ break;
+ }
+ }
+
+ tcmu_set_next_deadline(&udev->qfull_queue, &udev->qfull_timer);
+}
+
+static void tcmu_complete_work(struct work_struct *work)
+{
+ struct tcmu_dev *udev = container_of(work, struct tcmu_dev, complete_work);
+
+ mutex_lock(&udev->cmdr_lock);
+ if (tcmu_handle_completions(udev))
+ run_qfull_queue(udev, false);
+ mutex_unlock(&udev->cmdr_lock);
+}
+
static struct se_device *tcmu_alloc_device(struct se_hba *hba, const char *name)
{
struct tcmu_dev *udev;
@@ -1634,6 +1707,7 @@ static struct se_device *tcmu_alloc_device(struct se_hba *hba, const char *name)

xa_init(&udev->data_pages);

+ INIT_WORK(&udev->complete_work, tcmu_complete_work);
return &udev->se_dev;
}

@@ -1725,75 +1799,10 @@ static void tcmu_dev_kref_release(struct kref *kref)
call_rcu(&dev->rcu_head, tcmu_dev_call_rcu);
}

-static void run_qfull_queue(struct tcmu_dev *udev, bool fail)
-{
- struct tcmu_cmd *tcmu_cmd, *tmp_cmd;
- LIST_HEAD(cmds);
- sense_reason_t scsi_ret;
- int ret;
-
- if (list_empty(&udev->qfull_queue))
- return;
-
- pr_debug("running %s's cmdr queue forcefail %d\n", udev->name, fail);
-
- list_splice_init(&udev->qfull_queue, &cmds);
-
- list_for_each_entry_safe(tcmu_cmd, tmp_cmd, &cmds, queue_entry) {
- list_del_init(&tcmu_cmd->queue_entry);
-
- pr_debug("removing cmd %p on dev %s from queue\n",
- tcmu_cmd, udev->name);
-
- if (fail) {
- /*
- * We were not able to even start the command, so
- * fail with busy to allow a retry in case runner
- * was only temporarily down. If the device is being
- * removed then LIO core will do the right thing and
- * fail the retry.
- */
- tcmu_cmd->se_cmd->priv = NULL;
- target_complete_cmd(tcmu_cmd->se_cmd, SAM_STAT_BUSY);
- tcmu_free_cmd(tcmu_cmd);
- continue;
- }
-
- ret = queue_cmd_ring(tcmu_cmd, &scsi_ret);
- if (ret < 0) {
- pr_debug("cmd %p on dev %s failed with %u\n",
- tcmu_cmd, udev->name, scsi_ret);
- /*
- * Ignore scsi_ret for now. target_complete_cmd
- * drops it.
- */
- tcmu_cmd->se_cmd->priv = NULL;
- target_complete_cmd(tcmu_cmd->se_cmd,
- SAM_STAT_CHECK_CONDITION);
- tcmu_free_cmd(tcmu_cmd);
- } else if (ret > 0) {
- pr_debug("ran out of space during cmdr queue run\n");
- /*
- * cmd was requeued, so just put all cmds back in
- * the queue
- */
- list_splice_tail(&cmds, &udev->qfull_queue);
- break;
- }
- }
-
- tcmu_set_next_deadline(&udev->qfull_queue, &udev->qfull_timer);
-}
-
static int tcmu_irqcontrol(struct uio_info *info, s32 irq_on)
{
struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info);
-
- mutex_lock(&udev->cmdr_lock);
- if (tcmu_handle_completions(udev))
- run_qfull_queue(udev, false);
- mutex_unlock(&udev->cmdr_lock);
-
+ queue_work(tcmu_comp_wq, &udev->complete_work);
return 0;
}

@@ -3281,12 +3290,17 @@ static int __init tcmu_module_init(void)

INIT_DELAYED_WORK(&tcmu_unmap_work, tcmu_unmap_work_fn);

+ tcmu_comp_wq = alloc_workqueue("tcmu-comp-wq",
+ WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+ if (!tcmu_comp_wq)
+ return -ENOMEM;
+
tcmu_cmd_cache = kmem_cache_create("tcmu_cmd_cache",
sizeof(struct tcmu_cmd),
__alignof__(struct tcmu_cmd),
0, NULL);
if (!tcmu_cmd_cache)
- return -ENOMEM;
+ goto out_free_comp_wq;

tcmu_root_device = root_device_register("tcm_user");
if (IS_ERR(tcmu_root_device)) {
@@ -3335,6 +3349,8 @@ static int __init tcmu_module_init(void)
root_device_unregister(tcmu_root_device);
out_free_cache:
kmem_cache_destroy(tcmu_cmd_cache);
+out_free_comp_wq:
+ destroy_workqueue(tcmu_comp_wq);

return ret;
}
@@ -3347,6 +3363,7 @@ static void __exit tcmu_module_exit(void)
genl_unregister_family(&tcmu_genl_family);
root_device_unregister(tcmu_root_device);
kmem_cache_destroy(tcmu_cmd_cache);
+ destroy_workqueue(tcmu_comp_wq);
}

MODULE_DESCRIPTION("TCM USER subsystem plugin");
--
1.8.3.1