[Mesa-dev] [PATCH] i965: Fix batch-last mode to properly swap BOs.

[Lionel Landwerlin]

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>

On 04/06/18 11:18, Kenneth Graunke wrote:
> On pre-4.13 kernels, which don't support I915_EXEC_BATCH_FIRST, we move
> the validation list entry to the end...but incorrectly left the exec_bo
> array alone, causing a mismatch where exec_bos[0] no longer corresponded
> with validation_list[0] (and similarly for the last entry).
>
> One example of resulting breakage is that we'd update bo->gtt_offset
> based on the wrong buffer.  This wreaked total havoc when trying to use
> softpin, and likely caused unnecessary relocations in the normal case.
>
> Fixes: 29ba502a4e28471f67e4e904ae503157087efd20 (i965: Use I915_EXEC_BATCH_FIRST when available.)
> ---
>   src/mesa/drivers/dri/i965/intel_batchbuffer.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.c b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> index 2cee2376c0e..462789e8cfb 100644
> --- a/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> +++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> @@ -798,11 +798,16 @@ submit_batch(struct brw_context *brw, int in_fence_fd, int *out_fence_fd)
>         } else {
>            /* Move the batch to the end of the validation list */
>            struct drm_i915_gem_exec_object2 tmp;
> +         struct brw_bo *tmp_bo;
>            const unsigned index = batch->exec_count - 1;
>   
>            tmp = *entry;
>            *entry = batch->validation_list[index];
>            batch->validation_list[index] = tmp;
> +
> +         tmp_bo = batch->exec_bos[0];
> +         batch->exec_bos[0] = batch->exec_bos[index];
> +         batch->exec_bos[index] = tmp_bo;
>         }
>   
>         ret = execbuffer(dri_screen->fd, batch, brw->hw_ctx,