On Wed, Nov 27, 2024 at 5:20 AM [off-list ref] wrote:

On 11/5/24 1:25 AM, Cindy Lu wrote:

quoted

 static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
 {
      struct vhost_worker *worker;
-     struct vhost_task *vtsk;
+     struct vhost_task *vtsk = NULL;
+     struct task_struct *task = NULL;
      char name[TASK_COMM_LEN];
      int ret;
      u32 id;

+     /* Allocate resources for the worker */
      worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
      if (!worker)
              return NULL;

+     worker->fn = kzalloc(sizeof(struct vhost_task_fn), GFP_KERNEL_ACCOUNT);
+     if (!worker->fn) {
+             kfree(worker);
+             return NULL;
+     }

Why dynamically allocate this?

You could probably even just kill the vhost_task_fn struct since we just
have to the 2 callouts.

sure, will change this

quoted

+
      worker->dev = dev;
      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 (dev->inherit_owner) {
+             /* Create and start a vhost task */

Maybe instead of this comment and the one below write something about
what inherit_owner means. We can see from the code we are creating a
vhost/kthread, but it's not really obvious why. Something like:

/*
 * 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.
 */

Thanks, Mike， I will change this

quoted

+             vtsk = vhost_task_create(vhost_run_work_list,
+                                      vhost_worker_killed, worker, name);
+             if (!vtsk)
+                     goto free_worker;
+
+             worker->vtsk = vtsk;
+             worker->fn->wakeup = vhost_task_wakeup_fn;
+             worker->fn->stop = vhost_task_stop_fn;
+
+             vhost_task_start(vtsk);
+     } else {
+             /* Create and start a kernel thread */
+             task = kthread_create(vhost_run_work_kthread_list, worker,
+                                   "vhost-%d", current->pid);
+             if (IS_ERR(task)) {
+                     ret = PTR_ERR(task);
+                     goto free_worker;
+             }
+             worker->task = task;
+             worker->fn->wakeup = vhost_kthread_wakeup_fn;
+             worker->fn->stop = vhost_kthread_stop_fn;
+
+             wake_up_process(task);
+             /* Attach to the vhost cgroup */

You don't need this comment do you? The function name tells us the same
info.

sure, Will remove  this

quoted

+             ret = vhost_attach_cgroups(dev);

I don't think this works. Patch 3/9 did:

+       xa_for_each(&dev->worker_xa, i, worker) {
+               ret = vhost_worker_cgroups_kthread(worker);

but we don't add the worker to the xa until below.

You also want to just call vhost_worker_cgroups_kthread above, because
you only want to add the one task and not loop over all of them.

I would then also maybe rename vhost_worker_cgroups_kthread to something
like vhost_attach_task_to_cgroups.

Will fix this. Thanks

quoted

+             if (ret)
+                     goto stop_worker;
+     }

      ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
      if (ret < 0)
              goto stop_worker;
      worker->id = id;
-
      return worker;
-
 stop_worker:
-     vhost_task_stop(vtsk);
+     worker->fn->stop(dev->inherit_owner ? (void *)vtsk : (void *)task);

I don't think you need to cast since the function takes a void pointer.
Same comment for the other patches like 6/9 where you are calling the
callout and casting.

Sure, Thanks I will rewrite this part
Thanks
cindy