Re: [PATCH] target: add iscsi/cpus_allowed_list in configfs

From: Mike Christie <michael.christie@oracle.com>
To: mingzhe.zou@easystack.cn, martin.petersen@oracle.com,
	linux-scsi@vger.kernel.org, target-devel@vger.kernel.org
Subject: Re: [PATCH] target: add iscsi/cpus_allowed_list in configfs
Date: Tue, 8 Feb 2022 11:50:11 -0600	[thread overview]
Message-ID: <7234209a-d308-622b-700e-e72907246ff4@oracle.com> (raw)
In-Reply-To: <20220125083821.18225-1-mingzhe.zou@easystack.cn>

On 1/25/22 2:38 AM, mingzhe.zou@easystack.cn wrote:
> From: Mingzhe Zou <mingzhe.zou@easystack.cn>
> 
> The RX/TX threads for iSCSI connection can be scheduled to
> any online cpus, and will not be rescheduled.
> 
> If bind other heavy load threads with iSCSI connection
> RX/TX thread to the same cpu, the iSCSI performance will
> be worse.
> 
> This patch add iscsi/cpus_allowed_list in configfs. The
> available cpus set of iSCSI connection RX/TX threads is
> allowed_cpus & online_cpus. If it is modified, all RX/TX
> threads will be rescheduled.
> 
> Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>
> ---
>  drivers/target/iscsi/iscsi_target.c          | 21 ++++++++++--
>  drivers/target/iscsi/iscsi_target.h          | 17 ++++++++++
>  drivers/target/iscsi/iscsi_target_configfs.c | 34 ++++++++++++++++++++
>  drivers/target/iscsi/iscsi_target_login.c    |  7 ++++
>  include/target/iscsi/iscsi_target_core.h     |  1 +
>  5 files changed, 78 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
> index 2c54c5d8412d..a18d3fc3cfd1 100644
> --- a/drivers/target/iscsi/iscsi_target.c
> +++ b/drivers/target/iscsi/iscsi_target.c
> @@ -693,6 +693,11 @@ static int __init iscsi_target_init_module(void)
>  	mutex_init(&auth_id_lock);
>  	idr_init(&tiqn_idr);
>  
> +	/*
> +	 * allow all cpus run iscsi_ttx and iscsi_trx

I would just drop the comment. The "setall" in the function name
is pretty clear already.

> +	 */
> +	cpumask_setall(&__iscsi_allowed_cpumask);
> +
>  	ret = target_register_template(&iscsi_ops);
>  	if (ret)
>  		goto out;
> @@ -3587,6 +3592,15 @@ static int iscsit_send_reject(
>  void iscsit_thread_get_cpumask(struct iscsi_conn *conn)
>  {
>  	int ord, cpu;
> +	cpumask_t conn_allowed_cpumask;
> +
> +	/*
> +	 * The available cpus set of iSCSI connection's RX/TX threads
> +	 */

Probably can drop the comment too since the variable names make it
known what we are doing.

> +	cpumask_and(&conn_allowed_cpumask,
> +		&__iscsi_allowed_cpumask,
> +		cpu_online_mask);

The formatting needs some fix ups. I think __iscsi_allowed_cpumask can fit on the
line above it and then cpu_online_mask should be moved over a couple spaces to
align with the opening "(".

> +
>  	/*
>  	 * bitmap_id is assigned from iscsit_global->ts_bitmap from
>  	 * within iscsit_start_kthreads()
> @@ -3595,8 +3609,9 @@ void iscsit_thread_get_cpumask(struct iscsi_conn *conn)
>  	 * iSCSI connection's RX/TX threads will be scheduled to
>  	 * execute upon.
>  	 */
> -	ord = conn->bitmap_id % cpumask_weight(cpu_online_mask);
> -	for_each_online_cpu(cpu) {
> +	cpumask_clear(conn->conn_cpumask);
> +	ord = conn->bitmap_id % cpumask_weight(&conn_allowed_cpumask);
> +	for_each_cpu(cpu, &conn_allowed_cpumask) {
>  		if (ord-- == 0) {
>  			cpumask_set_cpu(cpu, conn->conn_cpumask);
>  			return;
> @@ -3821,6 +3836,7 @@ int iscsi_target_tx_thread(void *arg)
>  		 * Ensure that both TX and RX per connection kthreads
>  		 * are scheduled to run on the same CPU.
>  		 */
> +		iscsit_thread_reschedule(conn);

If we have multiple sessions to the same portal, could we end up racing
where session0's tx/rx threads call iscsit_thread_reschedule and
iscsit_thread_check_cpumask at the same time as session1's threads and
they end up taking the same cpus. They both could be running
iscsit_thread_get_cpumask at the same time, see he same masks values
and in the for_each_cpu loop think the same cpu is free.

>  		iscsit_thread_check_cpumask(conn, current, 1);
>  
>  		wait_event_interruptible(conn->queues_wq,
> @@ -3966,6 +3982,7 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
>  		 * Ensure that both TX and RX per connection kthreads
>  		 * are scheduled to run on the same CPU.
>  		 */
> +		iscsit_thread_reschedule(conn);
>  		iscsit_thread_check_cpumask(conn, current, 0);
>  
>  		memset(&iov, 0, sizeof(struct kvec));
> diff --git a/drivers/target/iscsi/iscsi_target.h b/drivers/target/iscsi/iscsi_target.h
> index b35a96ded9c1..cb97a316d76d 100644
> --- a/drivers/target/iscsi/iscsi_target.h
> +++ b/drivers/target/iscsi/iscsi_target.h
> @@ -57,4 +57,21 @@ extern struct kmem_cache *lio_r2t_cache;
>  extern struct ida sess_ida;
>  extern struct mutex auth_id_lock;
>  
> +extern cpumask_t __iscsi_allowed_cpumask;

I would rename to:

iscsit_allowed_cpumask

> +
> +static inline void iscsit_thread_reschedule(struct iscsi_conn *conn)
> +{
> +	/*
> +	 * If __iscsi_allowed_cpumask modified, reschedule iSCSI connection's
> +	 * RX/TX threads update conn->allowed_cpumask.
> +	 */
> +	if (!cpumask_equal(&__iscsi_allowed_cpumask, conn->allowed_cpumask)) {
> +		iscsit_thread_get_cpumask(conn);
> +		conn->conn_tx_reset_cpumask = 1;
> +		conn->conn_rx_reset_cpumask = 1;
> +		cpumask_copy(conn->allowed_cpumask,
> +			&__iscsi_allowed_cpumask);

Fix up formatting like above.

> +	}
> +}
> +
>  #endif   /*** ISCSI_TARGET_H ***/
> diff --git a/drivers/target/iscsi/iscsi_target_configfs.c b/drivers/target/iscsi/iscsi_target_configfs.c
> index 2a9de24a8bbe..dc12b1695838 100644
> --- a/drivers/target/iscsi/iscsi_target_configfs.c
> +++ b/drivers/target/iscsi/iscsi_target_configfs.c
> @@ -1127,8 +1127,42 @@ static ssize_t lio_target_wwn_lio_version_show(struct config_item *item,
>  
>  CONFIGFS_ATTR_RO(lio_target_wwn_, lio_version);
>  
> +cpumask_t __iscsi_allowed_cpumask;

Maybe better to put this in iscsi_target.c with the other vars like
it.

> +
> +static ssize_t lio_target_wwn_cpus_allowed_list_show(
> +		struct config_item *item, char *page)
> +{
> +	return sprintf(page, "%*pbl\n",
> +		cpumask_pr_args(&__iscsi_allowed_cpumask));

Formatting like above.

> +}
> +
> +static ssize_t lio_target_wwn_cpus_allowed_list_store(
> +		struct config_item *item, const char *page, size_t count)
> +{
> +	int ret;
> +	char *orig;
> +	cpumask_t new_allowed_cpumask;
> +
> +	orig = kstrdup(page, GFP_KERNEL);
> +	if (!orig)
> +		return -ENOMEM;
> +
> +	cpumask_clear(&new_allowed_cpumask);
> +	ret = cpulist_parse(orig, &new_allowed_cpumask);

Are you supposed to do a zalloc_cpumask_var/free_cpumask_var before
using new_allowed_cpumask? It looks like other callers are doing it.

> +
> +	kfree(orig);
> +	if (ret != 0)
> +		return ret;
> +
> +	cpumask_copy(&__iscsi_allowed_cpumask, &new_allowed_cpumask);
> +	return count;
> +}
> +
> +CONFIGFS_ATTR(lio_target_wwn_, cpus_allowed_list);
> +
>  static struct configfs_attribute *lio_target_wwn_attrs[] = {
>  	&lio_target_wwn_attr_lio_version,
> +	&lio_target_wwn_attr_cpus_allowed_list,
>  	NULL,
>  };
>  
> diff --git a/drivers/target/iscsi/iscsi_target_login.c b/drivers/target/iscsi/iscsi_target_login.c
> index 1a9c50401bdb..910f35e4648a 100644
> --- a/drivers/target/iscsi/iscsi_target_login.c
> +++ b/drivers/target/iscsi/iscsi_target_login.c
> @@ -1129,8 +1129,15 @@ static struct iscsi_conn *iscsit_alloc_conn(struct iscsi_np *np)
>  		goto free_conn_ops;
>  	}
>  
> +	if (!zalloc_cpumask_var(&conn->allowed_cpumask, GFP_KERNEL)) {
> +		pr_err("Unable to allocate conn->allowed_cpumask\n");
> +		goto free_conn_cpumask;
> +	}

I think in iscsit_free_conn you need a:

free_cpumask_var(conn->allowed_cpumask);

to go with this allocation.

> +
>  	return conn;
>  
> +free_conn_cpumask:
> +	free_cpumask_var(conn->allowed_cpumask);

I think you wanted conn->conn_cpumask here.

>  free_conn_ops:
>  	kfree(conn->conn_ops);
>  put_transport:
> diff --git a/include/target/iscsi/iscsi_target_core.h b/include/target/iscsi/iscsi_target_core.h
> index 1eccb2ac7d02..c5e9cad187cf 100644
> --- a/include/target/iscsi/iscsi_target_core.h
> +++ b/include/target/iscsi/iscsi_target_core.h
> @@ -580,6 +580,7 @@ struct iscsi_conn {
>  	struct ahash_request	*conn_tx_hash;
>  	/* Used for scheduling TX and RX connection kthreads */
>  	cpumask_var_t		conn_cpumask;
> +	cpumask_var_t		allowed_cpumask;
>  	unsigned int		conn_rx_reset_cpumask:1;
>  	unsigned int		conn_tx_reset_cpumask:1;
>  	/* list_head of struct iscsi_cmd for this connection */