Re: [PATCH 02/11] target: add workqueue cmd submission helper

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On 2/4/21 03:41, Mike Christie wrote:
> loop and vhost-scsi do their target cmd submission from driver
> workqueues. This allows them to avoid an issue where the backend may
> block waiting for resources like tags/requests, mem/locks, etc
> and that ends up blocking their entire submission path and for the
> case of vhost-scsi both the submission and completion path.
>
> This patch adds a helper these drivers can use to submit from the
> lio workqueue. This code will then be extended in the next patches
> to fix the plugging of backend devices.
>
> Signed-off-by: Mike Christie <michael.christie@xxxxxxxxxx>
> ---
>  drivers/target/target_core_transport.c | 102 ++++++++++++++++++++++++-
>  include/target/target_core_base.h      |  10 ++-
>  include/target/target_core_fabric.h    |   3 +
>  3 files changed, 111 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 7c5d37bac561..dec89e911348 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -41,6 +41,7 @@
>  #include <trace/events/target.h>
>  
>  static struct workqueue_struct *target_completion_wq;
> +static struct workqueue_struct *target_submission_wq;
>  static struct kmem_cache *se_sess_cache;
>  struct kmem_cache *se_ua_cache;
>  struct kmem_cache *t10_pr_reg_cache;
> @@ -129,8 +130,15 @@ int init_se_kmem_caches(void)
>  	if (!target_completion_wq)
>  		goto out_free_lba_map_mem_cache;
>  
> +	target_submission_wq = alloc_workqueue("target_submission",
> +					       WQ_MEM_RECLAIM, 0);
> +	if (!target_submission_wq)
> +		goto out_free_completion_wq;
> +
>  	return 0;
>  
> +out_free_completion_wq:
> +	destroy_workqueue(target_completion_wq);
>  out_free_lba_map_mem_cache:
>  	kmem_cache_destroy(t10_alua_lba_map_mem_cache);
>  out_free_lba_map_cache:
> @@ -153,6 +161,7 @@ int init_se_kmem_caches(void)
>  
>  void release_se_kmem_caches(void)
>  {
> +	destroy_workqueue(target_submission_wq);
>  	destroy_workqueue(target_completion_wq);
>  	kmem_cache_destroy(se_sess_cache);
>  	kmem_cache_destroy(se_ua_cache);
> @@ -218,6 +227,69 @@ static void target_release_sess_cmd_refcnt(struct percpu_ref *ref)
>  	wake_up(&sess->cmd_count_wq);
>  }
>  
> +static void target_queued_submit_work(struct work_struct *work)
> +{
> +	struct se_sess_cmd_queue *sq =
> +				container_of(work, struct se_sess_cmd_queue,
> +					     work);
> +	struct se_session *se_sess = sq->se_sess;
> +	struct se_cmd *se_cmd, *next_cmd;
> +	struct llist_node *cmd_list;
> +
> +	cmd_list = llist_del_all(&sq->cmd_list);
> +	if (!cmd_list)
> +		/* Previous call took what we were queued to submit */
> +		return;
> +
> +	cmd_list = llist_reverse_order(cmd_list);
> +	llist_for_each_entry_safe(se_cmd, next_cmd, cmd_list, se_cmd_list)
> +		se_sess->tfo->submit_queued_cmd(se_cmd);
> +}
> +
> +static void target_queue_cmd_work(struct se_sess_cmd_queue *q,
> +				  struct se_cmd *se_cmd, int cpu)
> +{
> +	llist_add(&se_cmd->se_cmd_list, &q->cmd_list);
> +	queue_work_on(cpu, target_submission_wq, &q->work);
> +}
> +
> +/**
> + * target_queue_cmd_submit - queue a se_cmd to be executed from the lio wq
> + * @se_sess: cmd's session
> + * @cmd_list: cmd to queue
> + */
> +void target_queue_cmd_submit(struct se_session *se_sess, struct se_cmd *se_cmd)
> +{
> +	int cpu = smp_processor_id();
> +
> +	target_queue_cmd_work(&se_sess->sq[cpu], se_cmd, cpu);
> +}
> +EXPORT_SYMBOL_GPL(target_queue_cmd_submit);
> +
> +static void target_flush_queued_cmds(struct se_session *se_sess)
> +{
> +	int i;
> +
> +	if (!se_sess->sq)
> +		return;
> +
> +	for (i = 0; i < se_sess->q_cnt; i++)
> +		cancel_work_sync(&se_sess->sq[i].work);
> +}
> +
> +static void target_init_sess_cmd_queues(struct se_session *se_sess,
> +					struct se_sess_cmd_queue *q,
> +					void (*work_fn)(struct work_struct *work))
> +{
> +	int i;
> +
> +	for (i = 0; i < se_sess->q_cnt; i++) {
> +		init_llist_head(&q[i].cmd_list);
> +		INIT_WORK(&q[i].work, work_fn);
> +		q[i].se_sess = se_sess;
> +	}
> +}
> +
Can we opencode above function if there is only one caller ?
unless there is a specific reason to have it on its own which I failed to
understand.
>  /**
>   * transport_init_session - initialize a session object
>   * @tfo: target core fabric ops
> @@ -228,6 +300,8 @@ static void target_release_sess_cmd_refcnt(struct percpu_ref *ref)
>  int transport_init_session(const struct target_core_fabric_ops *tfo,
>  			   struct se_session *se_sess)
>  {
> +	int rc;
> +
>  	INIT_LIST_HEAD(&se_sess->sess_list);
>  	INIT_LIST_HEAD(&se_sess->sess_acl_list);
>  	spin_lock_init(&se_sess->sess_cmd_lock);
> @@ -235,13 +309,34 @@ int transport_init_session(const struct target_core_fabric_ops *tfo,
>  	init_completion(&se_sess->stop_done);
>  	atomic_set(&se_sess->stopped, 0);
>  	se_sess->tfo = tfo;
> -	return percpu_ref_init(&se_sess->cmd_count,
> -			       target_release_sess_cmd_refcnt, 0, GFP_KERNEL);
> +
> +	if (tfo->submit_queued_cmd) {
> +		se_sess->sq = kcalloc(nr_cpu_ids, sizeof(*se_sess->sq),
> +				      GFP_KERNEL);
> +		if (!se_sess->sq)
> +			return -ENOMEM;
> +
> +		se_sess->q_cnt = nr_cpu_ids;
> +		target_init_sess_cmd_queues(se_sess, se_sess->sq,
> +					    target_queued_submit_work);
> +	}
> +
> +	rc = percpu_ref_init(&se_sess->cmd_count,
> +			     target_release_sess_cmd_refcnt, 0, GFP_KERNEL);
> +	if (rc)
> +		goto free_sq;
> +
> +	return 0;
> +
> +free_sq:
> +	kfree(se_sess->sq);
> +	return rc;
>  }
>  EXPORT_SYMBOL(transport_init_session);
>  
>  void transport_uninit_session(struct se_session *se_sess)
>  {
> +	kfree(se_sess->sq);
>  	/*
>  	 * Drivers like iscsi and loop do not call target_stop_session
>  	 * during session shutdown so we have to drop the ref taken at init
> @@ -1385,7 +1480,6 @@ void transport_init_se_cmd(
>  {
>  	INIT_LIST_HEAD(&cmd->se_delayed_node);
>  	INIT_LIST_HEAD(&cmd->se_qf_node);
> -	INIT_LIST_HEAD(&cmd->se_cmd_list);
>  	INIT_LIST_HEAD(&cmd->state_list);
>  	init_completion(&cmd->t_transport_stop_comp);
>  	cmd->free_compl = NULL;
> @@ -2968,6 +3062,8 @@ void target_wait_for_sess_cmds(struct se_session *se_sess)
>  {
>  	int ret;
>  
> +	target_flush_queued_cmds(se_sess);
> +
>  	WARN_ON_ONCE(!atomic_read(&se_sess->stopped));
>  
>  	do {
> diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
> index 50103a22b0e2..97138bff14d1 100644
> --- a/include/target/target_core_base.h
> +++ b/include/target/target_core_base.h
> @@ -488,7 +488,7 @@ struct se_cmd {
>  	/* Only used for internal passthrough and legacy TCM fabric modules */
>  	struct se_session	*se_sess;
>  	struct se_tmr_req	*se_tmr_req;
> -	struct list_head	se_cmd_list;
> +	struct llist_node	se_cmd_list;
>  	struct completion	*free_compl;
>  	struct completion	*abrt_compl;
>  	const struct target_core_fabric_ops *se_tfo;
> @@ -612,6 +612,12 @@ static inline struct se_node_acl *fabric_stat_to_nacl(struct config_item *item)
>  			acl_fabric_stat_group);
>  }
>  
> +struct se_sess_cmd_queue {
> +	struct llist_head	cmd_list;
> +	struct work_struct	work;
> +	struct se_session	*se_sess;
> +};
> +
>  struct se_session {
>  	atomic_t		stopped;
>  	u64			sess_bin_isid;
> @@ -629,6 +635,8 @@ struct se_session {
>  	void			*sess_cmd_map;
>  	struct sbitmap_queue	sess_tag_pool;
>  	const struct target_core_fabric_ops *tfo;
> +	struct se_sess_cmd_queue *sq;
> +	int			q_cnt;
>  };
>  
>  struct se_device;
> diff --git a/include/target/target_core_fabric.h b/include/target/target_core_fabric.h
> index cdf610838ba5..899948967a65 100644
> --- a/include/target/target_core_fabric.h
> +++ b/include/target/target_core_fabric.h
> @@ -80,6 +80,7 @@ struct target_core_fabric_ops {
>  	int (*queue_status)(struct se_cmd *);
>  	void (*queue_tm_rsp)(struct se_cmd *);
>  	void (*aborted_task)(struct se_cmd *);
> +	void (*submit_queued_cmd)(struct se_cmd *);
>  	/*
>  	 * fabric module calls for target_core_fabric_configfs.c
>  	 */
> @@ -166,6 +167,8 @@ int	target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
>  		unsigned char *sense, u64 unpacked_lun,
>  		void *fabric_tmr_ptr, unsigned char tm_type,
>  		gfp_t, u64, int);
> +void	target_queue_cmd_submit(struct se_session *se_sess,
> +				struct se_cmd *se_cmd);
>  int	transport_handle_cdb_direct(struct se_cmd *);
>  sense_reason_t	transport_generic_new_cmd(struct se_cmd *);
>  





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