On 11 July 2012 11:01, Chad Versace <chad.vers...@linux.intel.com> wrote:
> On 07/06/2012 03:29 PM, Paul Berry wrote:
> > This patch updates the blorp engine to properly handle the case where
> > the surface being textured from uses Gen7's CMS MSAA layout. The
> > following changes were necessary:
> >
> > - Before reading color values from the surface, we need to read from
> > the MCS buffer using the ld_mcs sampler message. This is done by
> > the mcs_fetch() function, and the result is stored in the mcs_data
> > register. This only needs to be done once per pixel, since the MCS
> > value is shared between all samples belonging to a pixel.
> >
> > - When reading color values from the surface, we need to use the
> > ld2dms sampler message instead of the ld2dss message, and we need to
> > provide the value read from the MCS buffer as an argument.
> > ---
> > src/mesa/drivers/dri/i965/brw_blorp_blit.cpp | 45
> ++++++++++++++++++++++++-
> > 1 files changed, 43 insertions(+), 2 deletions(-)
>
> I see an easy optimization that's suitable for a small follow-up patch.
> But this
> code works and passes tests, so let's commit it as-is first.
>
Cool. I'm curious to hear what your optimization idea is.
>
> This patch is
> Reviewed-by: Chad Versace <chad.vers...@linux.intel.com>
>
> > @@ -1126,8 +1148,13 @@ brw_blorp_blit_program::texel_fetch(struct
> brw_reg dst)
> > break;
> > case 7:
> > if (key->tex_samples > 0) {
> > - texture_lookup(dst, GEN7_SAMPLER_MESSAGE_SAMPLE_LD2DSS,
> > - gen7_ld2dss_args, ARRAY_SIZE(gen7_ld2dss_args));
> > + if (key->tex_layout == INTEL_MSAA_LAYOUT_CMS) {
> > + texture_lookup(dst, GEN7_SAMPLER_MESSAGE_SAMPLE_LD2DMS,
> > + gen7_ld2dms_args,
> ARRAY_SIZE(gen7_ld2dms_args));
> > + } else {
> > + texture_lookup(dst, GEN7_SAMPLER_MESSAGE_SAMPLE_LD2DSS,
> > + gen7_ld2dss_args,
> ARRAY_SIZE(gen7_ld2dss_args));
> > + }
>
> The hw docs suggest here "a simple optimization with probable large return
> in
> performance". If mcs_data == 0, which should be the common case for most
> fragments, then only sample array slice 0 needs to be accessed. That is,
> when
> tex_layout is CMS then we should emit code like this here:
>
> if (mcs_data == 0) {
> ld2dss(S, X, Y);
> } else {
> ld2dms(S, mcs_data, X, Y);
> }
>
I actually believe this will be slightly faster:
ld2dms(0, mcs_data, X, Y);
if (mcs_data != 0) {
for (S = 1; S < num_samples; ++S)
ld2dms(S, mcs_data, X, Y);
average samples together;
}
}
Because it will avoid issuing an extra sample instruction in the case where
some pixels have a zero value for mcs_data and others have a nonzero value
for mcs_data. I've got that queued up for a patch series after this one is
reviewed :)
>
> ----
> Chad Versace
> chad.vers...@linux.intel.com
>
>
>
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