Re: [RFC 16/20] drm/xe: Remove mem_access calls from migration

[Matthew Auld <matthew.auld@intel.com>]

On 28/12/2023 02:12, Rodrigo Vivi wrote:
> The sched jobs runtime pm calls already protects every execution,
> including these migration ones.

Is job really enough here? I assume queue is only destroyed once it has 
no more jobs and the final queue ref is dropped. And destroying the 
queue might involve stuff like de-register the context with GuC etc. 
which needs to use CT which will need rpm ref. What is holding the rpm 
if not the vm or queue?

> 
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
>   drivers/gpu/drm/xe/tests/xe_migrate.c |  2 --
>   drivers/gpu/drm/xe/xe_device.c        | 17 -----------------
>   drivers/gpu/drm/xe/xe_device.h        |  1 -
>   drivers/gpu/drm/xe/xe_exec_queue.c    | 18 ------------------
>   4 files changed, 38 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/tests/xe_migrate.c b/drivers/gpu/drm/xe/tests/xe_migrate.c
> index 7a32faa2f6888..2257f0a28435b 100644
> --- a/drivers/gpu/drm/xe/tests/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/tests/xe_migrate.c
> @@ -428,9 +428,7 @@ static int migrate_test_run_device(struct xe_device *xe)
>   
>   		kunit_info(test, "Testing tile id %d.\n", id);
>   		xe_vm_lock(m->q->vm, true);
> -		xe_device_mem_access_get(xe);
>   		xe_migrate_sanity_test(m, test);
> -		xe_device_mem_access_put(xe);
>   		xe_vm_unlock(m->q->vm);
>   	}
>   
> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> index ee9b6612eec43..a7bec49da49fa 100644
> --- a/drivers/gpu/drm/xe/xe_device.c
> +++ b/drivers/gpu/drm/xe/xe_device.c
> @@ -675,23 +675,6 @@ void xe_device_assert_mem_access(struct xe_device *xe)
>   	XE_WARN_ON(xe_pm_runtime_suspended(xe));
>   }
>   
> -bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe)
> -{
> -	bool active;
> -
> -	if (xe_pm_read_callback_task(xe) == current)
> -		return true;
> -
> -	active = xe_pm_runtime_get_if_active(xe);
> -	if (active) {
> -		int ref = atomic_inc_return(&xe->mem_access.ref);
> -
> -		xe_assert(xe, ref != S32_MAX);
> -	}
> -
> -	return active;
> -}
> -
>   void xe_device_mem_access_get(struct xe_device *xe)
>   {
>   	int ref;
> diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
> index af8ac2e9e2709..4acf4c2973390 100644
> --- a/drivers/gpu/drm/xe/xe_device.h
> +++ b/drivers/gpu/drm/xe/xe_device.h
> @@ -142,7 +142,6 @@ static inline struct xe_force_wake *gt_to_fw(struct xe_gt *gt)
>   }
>   
>   void xe_device_mem_access_get(struct xe_device *xe);
> -bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe);
>   void xe_device_mem_access_put(struct xe_device *xe);
>   
>   void xe_device_assert_mem_access(struct xe_device *xe);
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
> index 44fe8097b7cda..d3a8d2d8caaaf 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
> @@ -87,17 +87,6 @@ static struct xe_exec_queue *__xe_exec_queue_create(struct xe_device *xe,
>   	if (err)
>   		goto err_lrc;
>   
> -	/*
> -	 * Normally the user vm holds an rpm ref to keep the device
> -	 * awake, and the context holds a ref for the vm, however for
> -	 * some engines we use the kernels migrate vm underneath which offers no
> -	 * such rpm ref, or we lack a vm. Make sure we keep a ref here, so we
> -	 * can perform GuC CT actions when needed. Caller is expected to have
> -	 * already grabbed the rpm ref outside any sensitive locks.
> -	 */
> -	if (!(q->flags & EXEC_QUEUE_FLAG_PERMANENT) && (q->flags & EXEC_QUEUE_FLAG_VM || !vm))
> -		drm_WARN_ON(&xe->drm, !xe_device_mem_access_get_if_ongoing(xe));
> -
>   	return q;
>   
>   err_lrc:
> @@ -172,8 +161,6 @@ void xe_exec_queue_fini(struct xe_exec_queue *q)
>   
>   	for (i = 0; i < q->width; ++i)
>   		xe_lrc_finish(q->lrc + i);
> -	if (!(q->flags & EXEC_QUEUE_FLAG_PERMANENT) && (q->flags & EXEC_QUEUE_FLAG_VM || !q->vm))
> -		xe_device_mem_access_put(gt_to_xe(q->gt));
>   	if (q->vm)
>   		xe_vm_put(q->vm);
>   
> @@ -643,9 +630,6 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
>   			if (XE_IOCTL_DBG(xe, !hwe))
>   				return -EINVAL;
>   
> -			/* The migration vm doesn't hold rpm ref */
> -			xe_device_mem_access_get(xe);
> -
>   			migrate_vm = xe_migrate_get_vm(gt_to_tile(gt)->migrate);
>   			new = xe_exec_queue_create(xe, migrate_vm, logical_mask,
>   						   args->width, hwe,
> @@ -655,8 +639,6 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
>   						    EXEC_QUEUE_FLAG_BIND_ENGINE_CHILD :
>   						    0));
>   
> -			xe_device_mem_access_put(xe); /* now held by engine */
> -
>   			xe_vm_put(migrate_vm);
>   			if (IS_ERR(new)) {
>   				err = PTR_ERR(new);