[Mesa-dev] [PATCH] anv/blorp: sample input attachments with resolves on BDW

[Jason Ekstrand]

On Wed, Mar 22, 2017 at 7:38 AM, Samuel Iglesias Gonsálvez <
siglesias at igalia.com> wrote:

> On Tue, 2017-03-21 at 16:34 +0100, Samuel Iglesias Gonsálvez wrote:
> >
> > On 21/03/17 16:14, Jason Ekstrand wrote:
> > > On Tue, Mar 21, 2017 at 7:23 AM, Samuel Iglesias Gonsálvez
> > > <siglesias at igalia.com <mailto:siglesias at igalia.com>> wrote:
> > >
> > >     Input attachments are clear-color aware on Sky Lake, so we
> > >     can frequently sample from them with no resolves at all.
> > > However
> > >     on Broadwell we still need to do a a resolve between the
> > > subpass
> > >     that writes and the subpass that reads.
> > >
> > >
> > > In theory, we shouldn't always need to do a resolve.  Broadwell is
> > > supposed (maybe it doesn't work?) to support sampling from fast-
> > > cleared
> > > buffers and I thought it was hooked up correctly.  Is this only an
> > > issue
> > > for certain clear colors?  I have a feeling there's something more
> > > subtle going on here.
> > >
> >
> > OK, I will investigate further.
> >
>
> The value of the clear colors is irrelevant except if the image's clear
> color is the same than attachment's clear color, probably
> because sampling from fast-cleared buffers is not working and it has
> already the clear color it expects. Once they are different, the tests
> always fail.
>
> However, I think I have found something:
>
> According to BDW PRM, vol02d, RenderSurface::Auxiliary Surface Mode,
> the only available values are  AUX_NONE (0x0), AUX_MCS (0x1),
> AUX_APPEND (0x2), AUX_HIZ (0x3), the rest are reserved.
>
> AUX_MCS is only if the Auxiliary surface is an MCS (Multisample Control
> Surface). This is different in gen9+: set the mode to AUX_CCS_D (0x1)
> when the Auxiliary surface is a CCS (Color Control Surface) with
> compression disabled or an MCS with compression enabled, depending on
> Number of Multisamples.
>
> Inside color_attachment_compute_aux_usage() we are setting both aux
> surface usage and input aux usage to ISL_AUX_USAGE_CCS_D for BDW, but I
> think we need to do it only if it is a MCS (maybe set both to
> ISL_AUX_USAGE_MCS would be better?) and, if not, set the latter to
> ISL_AUX_USAGE_NONE in order to force the resolve in
> ccs_resolve_attachment() (see the first else-if of this patch).
>

Welcome to the subtlties of surface layout!  On Ivy Bridge through
Broadwell hardware, MCS is overloaded to mean both multisample compression
and fast-clears.  On Sky Lake, we have MCS, CCS_D, and CCS_E.  In ISL,
we've chosen to get rid of the aliasing and use CCS_D to mean single-sample
fast-clears on old hardware and keep MCS reserved for multisampling.  As
far as the Aux Usage field in SURFACE_STATE is concerned, both MCS and
CCS_D map to MCS.  See also isl_surface_state.c:90.


> What do you think?
>
> Sam
>
> >
> > >
> > >     Fixes 16 tests on BDW:
> > >
> > >     dEQP-VK.renderpass.formats.*.input.clear.store.self_dep*
> > >
> > >     Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com
> > >     <mailto:siglesias at igalia.com>>
> > >     ---
> > >      src/intel/vulkan/anv_blorp.c | 9 ++++++---
> > >      1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > >     diff --git a/src/intel/vulkan/anv_blorp.c
> > > b/src/intel/vulkan/anv_blorp.c
> > >     index 1f4fec5f35b..2fa56f49d18 100644
> > >     --- a/src/intel/vulkan/anv_blorp.c
> > >     +++ b/src/intel/vulkan/anv_blorp.c
> > >     @@ -1504,10 +1504,13 @@ ccs_resolve_attachment(struct
> > > anv_cmd_buffer
> > >     *cmd_buffer,
> > >                */
> > >            }
> > >         } else if (usage & ANV_SUBPASS_USAGE_INPUT) {
> > >     -      /* Input attachments are clear-color aware so, at least
> > > on
> > >     Sky Lake, we
> > >     -       * can frequently sample from them with no resolves at
> > > all.
> > >     +      /* Input attachments are clear-color aware on Sky Lake,
> > > so we
> > >     +       * can frequently sample from them with no resolves at
> > > all.
> > >     However
> > >     +       * on Broadwell we still need to do resolves.
> > >             */
> > >     -      if (att_state->aux_usage != att_state->input_aux_usage)
> > > {
> > >     +      if (cmd_buffer->device->info.gen < 9) {
> > >     +         resolve_op = BLORP_FAST_CLEAR_OP_RESOLVE_FULL;
> > >     +      } else if (att_state->aux_usage != att_state-
> > > >input_aux_usage) {
> > >               assert(att_state->input_aux_usage ==
> > > ISL_AUX_USAGE_NONE);
> > >               resolve_op = BLORP_FAST_CLEAR_OP_RESOLVE_FULL;
> > >            } else if (!att_state->clear_color_is_zero_one) {
> > >     --
> > >     2.11.0
> > >
> > >
> >
> >
>
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