On 09/03/2020 21:34, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2020-03-09 18:31:18)+struct i915_drm_client * +i915_drm_client_add(struct i915_drm_clients *clients, struct task_struct *task) +{ + struct i915_drm_client *client; + int ret; + + client = kzalloc(sizeof(*client), GFP_KERNEL); + if (!client) + return ERR_PTR(-ENOMEM); + + kref_init(&client->kref); + client->clients = clients; + + ret = mutex_lock_interruptible(&clients->lock); + if (ret) + goto err_id; + ret = xa_alloc_cyclic(&clients->xarray, &client->id, client, + xa_limit_32b, &clients->next_id, GFP_KERNEL);So what's next_id used for that explains having the over-arching mutex?
It's to give out client id's "cyclically" - before I apparently misunderstood what xa_alloc_cyclic is supposed to do - I thought after giving out id 1 it would give out 2 next, even if 1 was returned to the pool in the meantime. But it doesn't, I need to track the start point for the next search with "next".
I want this to make intel_gpu_top's life easier, so it doesn't have to deal with id recycling for all practical purposes.
And a peek into xa implementation told me the internal lock is not protecting "next.
I could stick with one lock and not use the internal one if I used it on release path as well.
Regards, Tvrtko _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
