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Message-ID: <CACGkMEvhiq2FWKZwPmemCMq-tcS=HG1MCs8Yyoj_EdOdPBQBHQ@mail.gmail.com>
Date: Mon, 24 Feb 2025 09:44:42 +0800
From: Jason Wang <jasowang@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: mst@...hat.com, michael.christie@...cle.com, sgarzare@...hat.com,
linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org
Subject: Re: [PATCH v6 4/6] vhost: introduce worker ops to support multiple
thread models
On Sun, Feb 23, 2025 at 11:41 PM Cindy Lu <lulu@...hat.com> wrote:
>
> This commit restores the previously removed functions kthread_wakeup and
> kthread_stop, and introduces a new ops structure to handle worker wakeup,
> stop, and creation. The function vhost_worker_create initializes these
> ops pointers based on the inherit_owner value.
>
> Signed-off-by: Cindy Lu <lulu@...hat.com>
Patch looks good but I have some some nits:
It might be better to have a separate patch to introduce the ops then
doing the kthread stuff on top.
> ---
> drivers/vhost/vhost.c | 115 +++++++++++++++++++++++++++++++++++-------
> drivers/vhost/vhost.h | 12 +++++
> 2 files changed, 110 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index adbb957c8b5f..d8c0ea118bb1 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);
> }
> }
>
> @@ -697,7 +697,7 @@ 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);
> }
>
> @@ -720,42 +720,123 @@ static void vhost_workers_free(struct vhost_dev *dev)
> xa_destroy(&dev->worker_xa);
> }
>
> +static void vhost_task_wakeup_fn(struct vhost_worker *worker)
> +{
> + return vhost_task_wake(worker->vtsk);
> +}
> +
> +static void vhost_kthread_wakeup_fn(struct vhost_worker *worker)
> +{
> + wake_up_process(worker->kthread_task);
> +}
> +
> +static void vhost_task_stop_fn(struct vhost_worker *worker)
> +{
> + return vhost_task_stop(worker->vtsk);
> +}
> +
> +static void vhost_kthread_stop_fn(struct vhost_worker *worker)
> +{
> + kthread_stop(worker->kthread_task);
> +}
> +
> +static int vhost_task_worker_create_fn(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 (!vtsk)
> + return -ENOMEM;
> +
> + 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_stop_fn(worker);
> + return ret;
> + }
> + worker->id = id;
> + return 0;
> +}
> +
> +static int kthread_worker_create_fn(struct vhost_worker *worker,
Let's have a consistent name, e.g vhost_kthread_worker_create.
> + struct vhost_dev *dev, const char *name)
> +{
> + struct task_struct *task;
> + u32 id;
> + int ret;
> +
> + task = kthread_create(vhost_run_work_kthread_list, worker, "%s", name);
> + if (IS_ERR(task))
> + return PTR_ERR(task);
> +
> + worker->kthread_task = task;
> + wake_up_process(task);
> + ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
> + if (ret < 0)
> + goto stop_worker;
> +
> + ret = vhost_attach_task_to_cgroups(worker);
> + if (ret)
> + goto stop_worker;
> +
> + worker->id = id;
> + return 0;
> +
> +stop_worker:
> + vhost_kthread_stop_fn(worker);
> + return ret;
> +}
> +
> +static const struct vhost_worker_ops vhost_task_ops = {
> + .create = vhost_task_worker_create_fn,
I think we can get rid of the fn suffix as "fn".
> + .stop = vhost_task_stop_fn,
> + .wakeup = vhost_task_wakeup_fn,
> +};
> +
> +static const struct vhost_worker_ops kthread_ops = {
> + .create = kthread_worker_create_fn,
> + .stop = vhost_kthread_stop_fn,
> + .wakeup = vhost_kthread_wakeup_fn,
> +};
> +
> 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 =
> + dev->inherit_owner ? &vhost_task_ops : &kthread_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 (!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);
> + /*
> + * If inherit_owner is true we use vhost_tasks to create
> + * the worker so all settings/limits like cgroups, NPROC,
> + * scheduler, etc are inherited from the owner. If false,
> + * we use kthreads and only attach to the same cgroups
> + * as the owner for compat with older kernels.
> + */
Is this better to move this to the definition of the inherit_owner?
>
> - 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 c650c4506c70..029c203147be 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -26,7 +26,18 @@ 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 task_struct *kthread_task;
> struct vhost_task *vtsk;
> struct vhost_dev *dev;
> /* Used to serialize device wide flushing with worker swapping. */
> @@ -36,6 +47,7 @@ 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
>
Thanks
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