Re: [PATCH v8 4/8] vhost: Introduce vhost_worker_ops in vhost_worker

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Mar 28, 2025 at 06:02:48PM +0800, Cindy Lu wrote:
> Abstract vhost worker operations (create/stop/wakeup) into an ops
> structure to prepare for kthread mode support.
> 
> Signed-off-by: Cindy Lu <lulu@redhat.com>

I worry about the overhead of indirect calls here.

We have the wrappers, and only two options,
why did you decide to add it like this,
with ops?



> ---
>  drivers/vhost/vhost.c | 63 ++++++++++++++++++++++++++++++-------------
>  drivers/vhost/vhost.h | 11 ++++++++
>  2 files changed, 56 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 20571bd6f7bd..c162ad772f8f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -243,7 +243,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
>  		 * test_and_set_bit() implies a memory barrier.
>  		 */
>  		llist_add(&work->node, &worker->work_list);
> -		vhost_task_wake(worker->vtsk);
> +		worker->ops->wakeup(worker);
>  	}
>  }
>  
> @@ -706,7 +706,7 @@ static void vhost_worker_destroy(struct vhost_dev *dev,
>  
>  	WARN_ON(!llist_empty(&worker->work_list));
>  	xa_erase(&dev->worker_xa, worker->id);
> -	vhost_task_stop(worker->vtsk);
> +	worker->ops->stop(worker);
>  	kfree(worker);
>  }
>  
> @@ -729,42 +729,69 @@ static void vhost_workers_free(struct vhost_dev *dev)
>  	xa_destroy(&dev->worker_xa);
>  }
>  
> +static void vhost_task_wakeup(struct vhost_worker *worker)
> +{
> +	return vhost_task_wake(worker->vtsk);
> +}
> +
> +static void vhost_task_do_stop(struct vhost_worker *worker)
> +{
> +	return vhost_task_stop(worker->vtsk);
> +}
> +
> +static int vhost_task_worker_create(struct vhost_worker *worker,
> +				    struct vhost_dev *dev, const char *name)
> +{
> +	struct vhost_task *vtsk;
> +	u32 id;
> +	int ret;
> +
> +	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
> +				 worker, name);
> +	if (IS_ERR(vtsk))
> +		return PTR_ERR(vtsk);
> +
> +	worker->vtsk = vtsk;
> +	vhost_task_start(vtsk);
> +	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
> +	if (ret < 0) {
> +		vhost_task_do_stop(worker);
> +		return ret;
> +	}
> +	worker->id = id;
> +	return 0;
> +}
> +
> +static const struct vhost_worker_ops vhost_task_ops = {
> +	.create = vhost_task_worker_create,
> +	.stop = vhost_task_do_stop,
> +	.wakeup = vhost_task_wakeup,
> +};
> +
>  static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
>  {
>  	struct vhost_worker *worker;
> -	struct vhost_task *vtsk;
>  	char name[TASK_COMM_LEN];
>  	int ret;
> -	u32 id;
> +	const struct vhost_worker_ops *ops = &vhost_task_ops;
>  
>  	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
>  	if (!worker)
>  		return NULL;
>  
>  	worker->dev = dev;
> +	worker->ops = ops;
>  	snprintf(name, sizeof(name), "vhost-%d", current->pid);
>  
> -	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
> -				 worker, name);
> -	if (IS_ERR(vtsk))
> -		goto free_worker;
> -
>  	mutex_init(&worker->mutex);
>  	init_llist_head(&worker->work_list);
>  	worker->kcov_handle = kcov_common_handle();
> -	worker->vtsk = vtsk;
> -
> -	vhost_task_start(vtsk);
> -
> -	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
> +	ret = ops->create(worker, dev, name);
>  	if (ret < 0)
> -		goto stop_worker;
> -	worker->id = id;
> +		goto free_worker;
>  
>  	return worker;
>  
> -stop_worker:
> -	vhost_task_stop(vtsk);
>  free_worker:
>  	kfree(worker);
>  	return NULL;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 19bb94922a0e..98895e299efa 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -26,6 +26,16 @@ struct vhost_work {
>  	unsigned long		flags;
>  };
>  
> +struct vhost_worker;
> +struct vhost_dev;
> +
> +struct vhost_worker_ops {
> +	int (*create)(struct vhost_worker *worker, struct vhost_dev *dev,
> +		      const char *name);
> +	void (*stop)(struct vhost_worker *worker);
> +	void (*wakeup)(struct vhost_worker *worker);
> +};
> +
>  struct vhost_worker {
>  	struct vhost_task	*vtsk;
>  	struct vhost_dev	*dev;
> @@ -36,6 +46,7 @@ struct vhost_worker {
>  	u32			id;
>  	int			attachment_cnt;
>  	bool			killed;
> +	const struct vhost_worker_ops *ops;
>  };
>  
>  /* Poll a file (eventfd or socket) */
> -- 
> 2.45.0