Re: [PATCH] drm/xe: Use bookkeep slots for external BO's in exec IOCTL

["Souza, Jose" <jose.souza@intel.com>]

On Wed, 2024-09-11 at 08:26 -0700, Matthew Brost wrote:
> Fix external BO's dma-resv usage in exec IOCTL using bookkeep slots
> rather than write slots. This leaves syncing to user space rather than
> the KMD blindly enforcing write semantics on every external BO.
> 

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>

> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Cc: José Roberto de Souza <jose.souza@intel.com>
> Cc: Kenneth Graunke <kenneth.w.graunke@intel.com>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Reported-by: Simona Vetter <simona.vetter@ffwll.ch>
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2673
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
> index 7b38485817dc..f23ac1e2ed88 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -41,11 +41,6 @@
>   * user knows an exec writes to a BO and reads from the BO in the next exec, it
>   * is the user's responsibility to pass in / out fence between the two execs).
>   *
> - * Implicit dependencies for external BOs are handled by using the dma-buf
> - * implicit dependency uAPI (TODO: add link). To make this works each exec must
> - * install the job's fence into the DMA_RESV_USAGE_WRITE slot of every external
> - * BO mapped in the VM.
> - *
>   * We do not allow a user to trigger a bind at exec time rather we have a VM
>   * bind IOCTL which uses the same in / out fence interface as exec. In that
>   * sense, a VM bind is basically the same operation as an exec from the user
> @@ -59,8 +54,8 @@
>   * behind any pending kernel operations on any external BOs in VM or any BOs
>   * private to the VM. This is accomplished by the rebinds waiting on BOs
>   * DMA_RESV_USAGE_KERNEL slot (kernel ops) and kernel ops waiting on all BOs
> - * slots (inflight execs are in the DMA_RESV_USAGE_BOOKING for private BOs and
> - * in DMA_RESV_USAGE_WRITE for external BOs).
> + * slots (inflight execs are in the DMA_RESV_USAGE_BOOKKEEP for private BOs and
> + * for external BOs).
>   *
>   * Rebinds / dma-resv usage applies to non-compute mode VMs only as for compute
>   * mode VMs we use preempt fences and a rebind worker (TODO: add link).
> @@ -304,7 +299,8 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  	xe_sched_job_arm(job);
>  	if (!xe_vm_in_lr_mode(vm))
>  		drm_gpuvm_resv_add_fence(&vm->gpuvm, exec, &job->drm.s_fence->finished,
> -					 DMA_RESV_USAGE_BOOKKEEP, DMA_RESV_USAGE_WRITE);
> +					 DMA_RESV_USAGE_BOOKKEEP,
> +					 DMA_RESV_USAGE_BOOKKEEP);
>  
>  	for (i = 0; i < num_syncs; i++) {
>  		xe_sync_entry_signal(&syncs[i], &job->drm.s_fence->finished);