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

Michael S. Tsirkin
2025-04-07T08:17:13Z

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