Re: [PATCH] drm/xe: Don't use drm exec locking in SVM pagefaults

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

On 2025-06-03 19:40, Matthew Brost wrote:
> Only the VM dma-resv lock is needed in SVM pagefaults so
> xe_vm_lock/unlock can be used instead of drm exec. Micro optimization
> but should save some CPU cycles in a critical path.
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c | 36 +++++++++++++-----------------------
>  1 file changed, 13 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index f27fb9b588de..952b75a4264d 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -858,7 +858,6 @@ int xe_svm_handle_pagefault(struct xe_vm *vm, struct xe_vma *vma,
>  			vm->xe->atomic_svm_timeslice_ms : 0,
>  	};
>  	struct xe_svm_range *range;
> -	struct drm_exec exec;
>  	struct dma_fence *fence;
>  	struct xe_tile *tile = gt_to_tile(gt);
>  	int migrate_try_count = ctx.devmem_only ? 3 : 1;
> @@ -933,30 +932,21 @@ int xe_svm_handle_pagefault(struct xe_vm *vm, struct xe_vma *vma,
>  	range_debug(range, "PAGE FAULT - BIND");
>  
>  retry_bind:
> -	drm_exec_init(&exec, 0, 0);
> -	drm_exec_until_all_locked(&exec) {
> -		err = drm_exec_lock_obj(&exec, vm->gpuvm.r_obj);
> -		drm_exec_retry_on_contention(&exec);
> -		if (err) {
> -			drm_exec_fini(&exec);
> -			goto err_out;
> -		}
> -
> -		fence = xe_vm_range_rebind(vm, vma, range, BIT(tile->id));
> -		if (IS_ERR(fence)) {
> -			drm_exec_fini(&exec);
> -			err = PTR_ERR(fence);
> -			if (err == -EAGAIN) {
> -				ctx.timeslice_ms <<= 1;	/* Double timeslice if we have to retry */
> -				range_debug(range, "PAGE FAULT - RETRY BIND");
> -				goto retry;
> -			}
> -			if (xe_vm_validate_should_retry(&exec, err, &end))
> -				goto retry_bind;
> -			goto err_out;
> +	xe_vm_lock(vm, false);
> +	fence = xe_vm_range_rebind(vm, vma, range, BIT(tile->id));
> +	if (IS_ERR(fence)) {
> +		xe_vm_unlock(vm);
> +		err = PTR_ERR(fence);
> +		if (err == -EAGAIN) {
> +			ctx.timeslice_ms <<= 1;	/* Double timeslice if we have to retry */
> +			range_debug(range, "PAGE FAULT - RETRY BIND");
> +			goto retry;
>  		}
> +		if (xe_vm_validate_should_retry(NULL, err, &end))
> +			goto retry_bind;
> +		goto err_out;
>  	}
> -	drm_exec_fini(&exec);
> +	xe_vm_unlock(vm);
>  
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>