[Mesa-dev] [PATCH 1/3] i965: Ensure that intel_bufferobj_map_range meets alignment guarantees

[Kenneth Graunke]

On 01/03/2014 04:51 PM, Ian Romanick wrote:
> From: Ian Romanick <ian.d.romanick at intel.com>
> 
> No piglit regressions on IVB.
> 
> With minor tweaks to the arb_map_buffer_alignment-map-invalidate-range
> test (disable the extension check, set alignment to 64 instead of
> querying), the i965 driver would fail the test without this patch (as
> predicted by Eric).  With this patch, it passes.
> 
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> Cc: Eric Anholt <eric at anholt.net>
> Cc: Siavash Eliasi <siavashserver at gmail.com>
> ---
>  src/mesa/drivers/dri/i965/intel_buffer_objects.c | 28 ++++++++++++++++++------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/intel_buffer_objects.c b/src/mesa/drivers/dri/i965/intel_buffer_objects.c
> index cab805a..7bf8cae 100644
> --- a/src/mesa/drivers/dri/i965/intel_buffer_objects.c
> +++ b/src/mesa/drivers/dri/i965/intel_buffer_objects.c
> @@ -359,20 +359,28 @@ intel_bufferobj_map_range(struct gl_context * ctx,
>      */
>     if ((access & GL_MAP_INVALIDATE_RANGE_BIT) &&
>         drm_intel_bo_busy(intel_obj->buffer)) {
> +      /* Ensure that the base alignment of the allocation meets the alignment
> +       * guarantees the driver has advertised to the application.
> +       */
> +      const unsigned alignment = MAX2(64, ctx->Const.MinMapBufferAlignment);

The MAX2(64, ...) seems like unnecessary complexity.  We want the
alignment to be ctx->Const.MinMapBufferAlignment (which should be bumped
to >= 64 in a follow on patch).

With that removed, patch 1 is:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

Nice work.

I'd love to see a follow-up patch that:
1. Sets ctx->Const.MinMapBufferAlignment to 64
   (in brw_context.c/brw_initialize_context_constants)
2. Enables the extension (in intel_extensions.c)

I know you'd like to turn it on for all drivers, but we may as well
claim victory here in the meantime.

> +      const unsigned extra = (uintptr_t) offset % alignment;
> +
>        if (access & GL_MAP_FLUSH_EXPLICIT_BIT) {
> -	 intel_obj->range_map_buffer = malloc(length);
> -	 obj->Pointer = intel_obj->range_map_buffer;
> +         intel_obj->range_map_buffer = _mesa_align_malloc(length + extra,
> +                                                          alignment);
> +         obj->Pointer = intel_obj->range_map_buffer + extra;
>        } else {
>  	 intel_obj->range_map_bo = drm_intel_bo_alloc(brw->bufmgr,
>  						      "range map",
> -						      length, 64);
> +                                                      length + extra,
> +                                                      alignment);
>  	 if (!(access & GL_MAP_READ_BIT)) {
>  	    drm_intel_gem_bo_map_gtt(intel_obj->range_map_bo);
>  	 } else {
>  	    drm_intel_bo_map(intel_obj->range_map_bo,
>  			     (access & GL_MAP_WRITE_BIT) != 0);
>  	 }
> -	 obj->Pointer = intel_obj->range_map_bo->virtual;
> +	 obj->Pointer = intel_obj->range_map_bo->virtual + extra;
>        }
>        return obj->Pointer;
>     }
> @@ -424,7 +432,11 @@ intel_bufferobj_flush_mapped_range(struct gl_context *ctx,
>  
>     temp_bo = drm_intel_bo_alloc(brw->bufmgr, "range map flush", length, 64);
>  
> -   drm_intel_bo_subdata(temp_bo, 0, length, intel_obj->range_map_buffer);
> +   /* Use obj->Pointer instead of intel_obj->range_map_buffer because the
> +    * former points to the actual mapping while the latter may be offset to
> +    * meet alignment guarantees.
> +    */
> +   drm_intel_bo_subdata(temp_bo, 0, length, obj->Pointer);
>  
>     intel_emit_linear_blit(brw,
>  			  intel_obj->buffer, obj->Offset + offset,
> @@ -456,14 +468,16 @@ intel_bufferobj_unmap(struct gl_context * ctx, struct gl_buffer_object *obj)
>         * usage inside of a batchbuffer.
>         */
>        intel_batchbuffer_emit_mi_flush(brw);
> -      free(intel_obj->range_map_buffer);
> +      _mesa_align_free(intel_obj->range_map_buffer);
>        intel_obj->range_map_buffer = NULL;
>     } else if (intel_obj->range_map_bo != NULL) {
> +      const unsigned extra = obj->Pointer - intel_obj->range_map_bo->virtual;
> +
>        drm_intel_bo_unmap(intel_obj->range_map_bo);
>  
>        intel_emit_linear_blit(brw,
>  			     intel_obj->buffer, obj->Offset,
> -			     intel_obj->range_map_bo, 0,
> +			     intel_obj->range_map_bo, extra,
>  			     obj->Length);
>        intel_bufferobj_mark_gpu_usage(intel_obj, obj->Offset, obj->Length);
>  
>