Re: [Intel-gfx] [PATCH] drm/i915/mtl: Increase guard pages when vt-d is enabled

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 02.11.2023 17:06, Radhakrishna Sripada wrote:
> Experiments were conducted with different multipliers to VTD_GUARD macro
> with multiplier of 185 we were observing occasional pipe faults when
> running kms_cursor_legacy --run-subtest single-bo
> 
> There could possibly be an underlying issue that is being investigated, for
> now bump the guard pages for MTL.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2017
> Cc: Gustavo Sousa <gustavo.sousa@intel.com>
> Cc: Chris Wilson <chris.p.wilson@linux.intel.com>
> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_domain.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> index 3770828f2eaf..b65f84c6bb3f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> @@ -456,6 +456,9 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>   	if (intel_scanout_needs_vtd_wa(i915)) {
>   		unsigned int guard = VTD_GUARD;
>   
> +		if (IS_METEORLAKE(i915))
> +			guard *= 200;
> +

200 * VTD_GUARD = 200 * 168 * 4K = 131MB

Looks insanely high, 131MB for padding, if this is before and after it 
becomes even 262MB of wasted address per plane. Just signalling, I do 
not know if this actually hurts.

Regards
Andrzej



>   		if (i915_gem_object_is_tiled(obj))
>   			guard = max(guard,
>   				    i915_gem_object_get_tile_row_size(obj));