[Mesa-dev] [PATCH 1/2] i965: Correct a mistake that always forced texture tiling.

[Ben Widawsky]

On Tue, Aug 04, 2015 at 11:16:55PM -0700, Matt Turner wrote:
> On Tue, Aug 4, 2015 at 11:18 PM, Matt Turner <mattst88 at gmail.com> wrote:
> > Regression since commit 3a31876600, when tiling modes were moved into
> > layout_flags.
> >
It be interesting to find out why this caused the perf regression.

> > The relevant enum values are
> >
> >    MIPTREE_LAYOUT_ALLOC_YTILED = 1 << 5
> >    MIPTREE_LAYOUT_ALLOC_XTILED = 1 << 6
> >    MIPTREE_LAYOUT_ALLOC_ANY_TILED = MIPTREE_LAYOUT_ALLOC_YTILED |
> >                                     MIPTREE_LAYOUT_ALLOC_XTILED
> >    MIPTREE_LAYOUT_ALLOC_LINEAR = 1 << 7
> >
> > so the expression (layout_flags & MIPTREE_LAYOUT_ALLOC_ANY_TILED) can
> > never produce a value of MIPTREE_LAYOUT_ALLOC_LINEAR.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91513
> > ---
> > I find this code really weird. MIPTREE_LAYOUT_ALLOC_XTILED is only used
> > in the two places noted in the commit message, and it wasn't an enum
> > value in the intel_miptree_tiling_mode type removed in the aforementioned
> > commit. Even with this patch, the brw_miptree_choose_tiling() function
> > wouldn't do anything sensible if passed XTILED | ~YTILED in layout_flags.
> > In fact, that case isn't even handled by the switch statement...
> >

I could imagine that being a problem pre-gen6, but I think once we had Y-tiling
and blitter support, we never actually use X-tiled except for the scanout
buffer. /me shrugs.

> >  src/mesa/drivers/dri/i965/brw_tex_layout.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > w
> > diff --git a/src/m esa/drivers/dri/i965/brw_tex_layout.c b/src/mesa/drivers/dri/i965/brw_tex_layout.c
> > index fb78b08..8f492e3 100644
> > --- a/src/mesa/drivers/dri/i965/brw_tex_layout.c
> > +++ b/src/mesa/drivers/dri/i965/brw_tex_layout.c
> > @@ -633,11 +633,11 @@ brw_miptree_choose_tiling(struct brw_context *brw,
> >     switch (layout_flags & MIPTREE_LAYOUT_ALLOC_ANY_TILED) {
> >     case MIPTREE_LAYOUT_ALLOC_ANY_TILED:
> >        break;
> >     case MIPTREE_LAYOUT_ALLOC_YTILED:
> >        return I915_TILING_Y;
> > -   case MIPTREE_LAYOUT_ALLOC_LINEAR:
> > +   case 0:
> 
> Maybe a better fix is to include LINEAR in the definition of ANY? I
> suspect that matches the previous behavior better than this.
> 

Hmm. Looking at the part you change it looks like what I meant. I do want any to
mean any type of tiling, Y, X, eventually Yf, and Ys. What about:

switch (layout_flags & (MIPTREE_LAYOUT_ALLOC_ANY_TILED | LINEAR))

I haven't had coffee yet. If that's no good I'll revisit it in a bit.


> >        return I915_TILING_NONE;
> >     }
> >
> >     if (mt->num_samples > 1) {
> >        /* From p82 of the Sandy Bridge PRM, dw3[1] of SURFACE_STATE ("Tiled
> > --
> > 2.3.6