[Mesa-dev] [PATCH 07/20] i965/fs: Import image memory offset calculation code.
Francisco Jerez
currojerez at riseup.net
Fri Jul 24 08:49:15 PDT 2015
Jason Ekstrand <jason at jlekstrand.net> writes:
> On Jul 24, 2015 8:02 AM, "Francisco Jerez" <currojerez at riseup.net> wrote:
>>
>> Jason Ekstrand <jason at jlekstrand.net> writes:
>>
>> > On Fri, Jul 24, 2015 at 7:39 AM, Francisco Jerez <currojerez at riseup.net>
> wrote:
>> >> Jason Ekstrand <jason at jlekstrand.net> writes:
>> >>
>> >>> On Jul 24, 2015 4:00 AM, "Francisco Jerez" <currojerez at riseup.net>
> wrote:
>> >>>>
>> >>>> Jason Ekstrand <jason at jlekstrand.net> writes:
>> >>>>
>> >>>> > Ok, I've looked through this again and convinced myself that it's
>> >>>> > *mostly* correct. I am a bit skeptical of the address swizzling
> for
>> >>>> > Y-major tiling.
>> >>>> >
>> >>>> > I've also included some comments that I'd like to see added
> (assuming
>> >>>> > they're correct). Sometimes it's easier to write helpful comments
> if
>> >>>> > the person who is confused does the writing. :-)
>> >>>> >
>> >>>>
>> >>>> Thanks! This will save me quite some guesswork, I'll add them to the
>> >>>> patch.
>> >>>>
>> >>>> > Also, I'd just like to say that I'm terribly impressed after
> reading
>> >>>> > through this. You managed to handle an amazing number of cases
>> >>>> > without so much as a single if statement or predicated instruction.
>> >>>> > My hat's off to you sir.
>> >>>> >
>> >>>> Hah, I feel flattered. :)
>> >>>>
>> >>>> > Modulo Y-tiling and comments,
>> >>>> >
>> >>>> > Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>
>> >>>> >
>> >>>> > On Tue, Jul 21, 2015 at 9:38 AM, Francisco Jerez <
> currojerez at riseup.net>
>> >>> wrote:
>> >>>> >> Define a function to calculate the memory address of the image
>> >>>> >> location given by a vector of coordinates. This is required in
> cases
>> >>>> >> where we need to fall back to untyped surface access, which take
> a raw
>> >>>> >> memory offset and know nothing about surface coordinates, type
>> >>>> >> conversion or memory tiling and swizzling. They are still useful
>> >>>> >> because typed surface reads don't support any 64 or 128-bit
> formats on
>> >>>> >> IVB, and they don't support any 128-bit formats on HSW and BDW.
>> >>>> >>
>> >>>> >> The tiling algorithm is implemented based on a number of
> parameters
>> >>>> >> which are passed in as uniforms and determine whether the surface
>> >>>> >> layout is X-tiled, Y-tiled or untiled. This allows binding
> surfaces
>> >>>> >> of different tiling layouts to the pipeline without recompiling
> the
>> >>>> >> program.
>> >>>> >>
>> >>>> >> v2: Drop VEC4 suport.
>> >>>> >> v3: Rebase.
>> >>>> >> ---
>> >>>> >> .../drivers/dri/i965/brw_fs_surface_builder.cpp | 108
>> >>> +++++++++++++++++++++
>> >>>> >> 1 file changed, 108 insertions(+)
>> >>>> >>
>> >>>> >> diff --git a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>> >>> b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>> >>>> >> index 5ee04de..0c879db 100644
>> >>>> >> --- a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>> >>>> >> +++ b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>> >>>> >> @@ -215,4 +215,112 @@ namespace {
>> >>>> >> return BRW_PREDICATE_NORMAL;
>> >>>> >> }
>> >>>> >> }
>> >>>> >> +
>> >>>> >> + namespace image_coordinates {
>> >>>> >> + /**
>> >>>> >> + * Calculate the offset in memory of the texel given by \p
>> >>> coord.
>> >>>> >> + *
>> >>>> >> + * This is meant to be used with untyped surface messages
> to
>> >>> access a
>> >>>> >> + * tiled surface, what involves taking into account the
> tiling
>> >>> and
>> >>>> >> + * swizzling modes of the surface manually so it will
> hopefully
>> >>> not
>> >>>> >> + * happen very often.
>> >>>> >> + */
>> >>>> >> + fs_reg
>> >>>> >> + emit_address_calculation(const fs_builder &bld, const
> fs_reg
>> >>> &image,
>> >>>> >> + const fs_reg &coord, unsigned
> dims)
>> >>>> >> + {
>> >>>> >> + const brw_device_info *devinfo = bld.shader->devinfo;
>> >>>> >> + const fs_reg off = offset(image, bld,
>> >>> BRW_IMAGE_PARAM_OFFSET_OFFSET);
>> >>>> >> + const fs_reg stride = offset(image, bld,
>> >>> BRW_IMAGE_PARAM_STRIDE_OFFSET);
>> >>>> >> + const fs_reg tile = offset(image, bld,
>> >>> BRW_IMAGE_PARAM_TILING_OFFSET);
>> >>>> >> + const fs_reg swz = offset(image, bld,
>> >>> BRW_IMAGE_PARAM_SWIZZLING_OFFSET);
>> >>>> >> + const fs_reg addr = bld.vgrf(BRW_REGISTER_TYPE_UD, 2);
>> >>>> >> + const fs_reg tmp = bld.vgrf(BRW_REGISTER_TYPE_UD, 2);
>> >>>> >> + const fs_reg minor = bld.vgrf(BRW_REGISTER_TYPE_UD, 2);
>> >>>> >> + const fs_reg major = bld.vgrf(BRW_REGISTER_TYPE_UD, 2);
>> >>>> >> + const fs_reg dst = bld.vgrf(BRW_REGISTER_TYPE_UD);
>> >>>> >> +
>> >>>> >> + /* Shift the coordinates by the fixed surface offset. */
>> >>>> >> + for (unsigned c = 0; c < 2; ++c)
>> >>>> >> + bld.ADD(offset(addr, bld, c), offset(off, bld, c),
>> >>>> >> + (c < dims ?
>> >>>> >> + offset(retype(coord, BRW_REGISTER_TYPE_UD),
> bld,
>> >>> c) :
>> >>>> >> + fs_reg(0)));
>> >>>> >> +
>> >>>> >> + if (dims > 2) {
>> >>>> >> + /* Decompose z into a major (tmp.y) and a minor
> (tmp.x)
>> >>>> >> + * index.
>> >>>> >
>> >>>> > Please add a comment:
>> >>>> > /*
>> >>>> > The layout of 3-D textures in memory is sort-of like a tiling
> format.
>> >>>> > At each miplevel, the slices are arranged in rows of 2^level slices
>> >>>> > per row. The slice row is stored in tmp.y and the slice within the
>> >>>> > row is stored in tmp.x. The layout of 2-D array textures is much
>> >>>> > simpler. Each slice of the texture is storred as a 2-D texture
> with
>> >>>> > all its miplevels and then one qpitch later, the next slice is
> stored
>> >>>> > with its miplevels. This code handles both by passing in the
> miplevel
>> >>>> > as tile[2] for 3-D textures and 0 in tile[2] for 2-D array
> textures.
>> >>>> > */
>> >>>>
>> >>>> Note that depending on the ARYSPC_LOD0 surface state flag array
> textures
>> >>>> may also be interleaved in the opposite way -- All slices for LOD0,
> then
>> >>>> all slices for LOD1, and so on. We probably don't hit this case
>> >>>> currently because MS images are not exposed but it's handled in the
> same
>> >>>> way by setting stride[3] to the spacing between slices. I'll add
> that
>> >>>> to your comment.
>> >>>>
>> >>>> >> + */
>> >>>> >> + bld.BFE(offset(tmp, bld, 0), offset(tile, bld, 2),
>> >>> fs_reg(0),
>> >>>> >> + offset(retype(coord, BRW_REGISTER_TYPE_UD),
> bld,
>> >>> 2));
>> >>>> >> + bld.SHR(offset(tmp, bld, 1),
>> >>>> >> + offset(retype(coord, BRW_REGISTER_TYPE_UD),
> bld,
>> >>> 2),
>> >>>> >> + offset(tile, bld, 2));
>> >>>> >> +
>> >>>> >> + /* Take into account the horizontal (tmp.x) and
> vertical
>> >>> (tmp.y)
>> >>>> >> + * slice offset.
>> >>>> >> + */
>> >>>> >> + for (unsigned c = 0; c < 2; ++c) {
>> >>>> >> + bld.MUL(offset(tmp, bld, c),
>> >>>> >> + offset(stride, bld, 2 + c), offset(tmp,
> bld,
>> >>> c));
>> >>>> >> + bld.ADD(offset(addr, bld, c),
>> >>>> >> + offset(addr, bld, c), offset(tmp, bld,
> c));
>> >>>> >> + }
>> >>>> >> + }
>> >>>> >> +
>> >>>> >> + if (dims > 1) {
>> >>>> >
>> >>>> > Please add as a comment:
>> >>>> > /*
>> >>>> > Calculate the major/minor x and y indices. In order to accommodate
>> >>>> > both X and Y tiling, the Y-major tiling format is treated as being
> a
>> >>>> > bunch of narrow X-tiles placed next to each other. This means
> that
>> >>>> > the tile width for Y-tiling is actually the width of one
> sub-column of
>> >>>> > the Y-major tile where each 4K tile has 8 512B sub-columns.
>> >>>> >
>> >>>> > The major Y value is the row of tiles in which the pixel lives.
> The
>> >>>> > major X value is the tile sub-column in which the pixel lives; for
> X
>> >>>> > tiling, this is the same as the tile column, for Y tiling, each
> tile
>> >>>> > has 8 sub-columns. The minor X and Y indices are the position
> within
>> >>>> > the sub-column.
>> >>>> > */
>> >>>> >> + for (unsigned c = 0; c < 2; ++c) {
>> >>>> >> + /* Calculate the minor x and y indices. */
>> >>>> >> + bld.BFE(offset(minor, bld, c), offset(tile, bld,
> c),
>> >>>> >> + fs_reg(0), offset(addr, bld, c));
>> >>>> >> +
>> >>>> >> + /* Calculate the major x and y indices. */
>> >>>> >> + bld.SHR(offset(major, bld, c),
>> >>>> >> + offset(addr, bld, c), offset(tile, bld,
> c));
>> >>>> >> + }
>> >>>> >> +
>> >>>> >> + /* Calculate the texel index from the start of the
> tile
>> >>> row and
>> >>>> >> + * the vertical coordinate of the row.
>> >>>> >> + * Equivalent to:
>> >>>> >> + * tmp.x = (major.x << tile.y << tile.x) +
>> >>>> >> + * (minor.y << tile.x) + minor.x
>> >>>> >> + * tmp.y = major.y << tile.y
>> >>>> >> + */
>> >>>> >> + bld.SHL(tmp, major, offset(tile, bld, 1));
>> >>>> >> + bld.ADD(tmp, tmp, offset(minor, bld, 1));
>> >>>> >> + bld.SHL(tmp, tmp, offset(tile, bld, 0));
>> >>>> >> + bld.ADD(tmp, tmp, minor);
>> >>>> >> + bld.SHL(offset(tmp, bld, 1),
>> >>>> >> + offset(major, bld, 1), offset(tile, bld, 1));
>> >>>> >> +
>> >>>> >> + /* Add it to the start of the tile row. */
>> >>>> >> + bld.MUL(offset(tmp, bld, 1),
>> >>>> >> + offset(tmp, bld, 1), offset(stride, bld, 1));
>> >>>> >> + bld.ADD(tmp, tmp, offset(tmp, bld, 1));
>> >>>> >> +
>> >>>> >> + /* Multiply by the Bpp value. */
>> >>>> >> + bld.MUL(dst, tmp, stride);
>> >>>> >> +
>> >>>> >> + if (devinfo->gen < 8 && !devinfo->is_baytrail) {
>> >>>> >
>> >>>> > Talking to Ken a bit about this. It seems as if this is actually
> the
>> >>>> > check we want. It's going to be a nasty bug if someone has a
> shader
>> >>>> > cache on a HSW machine, runs some compute shaders, pulls out a
> stick
>> >>>> > of ram (going from dual to single-channel), and starts it up again.
>> >>>> > Probably best to compile the shader the same regardless of how much
>> >>>> > ram you have.
>> >>>> >
>> >>>> Hmm, I guess we could also invalidate the cache if the flag changes?
>> >>>> (or in case anything else changes from the brw_device_info structure)
>> >>>>
>> >>>> >> + /* Take into account the two dynamically specified
>> >>> shifts. */
>> >>>> >> + for (unsigned c = 0; c < 2; ++c)
>> >>>> >> + bld.SHR(offset(tmp, bld, c), dst, offset(swz,
> bld,
>> >>> c));
>> >>>> >> +
>> >>>> >> + /* XOR tmp.x and tmp.y with bit 6 of the memory
>> >>> address. */
>> >>>> >> + bld.XOR(tmp, tmp, offset(tmp, bld, 1));
>> >>>> >> + bld.AND(tmp, tmp, fs_reg(1 << 6));
>> >>>> >> + bld.XOR(dst, dst, tmp);
>> >>>> >
>> >>>> > I don't think this is correct for Y-tiled surfaces. In Y-tiling,
> bit
>> >>>> > 6 of the address is given by bit6 XOR bit9. You have one extra XOR
>> >>>> > which means you just get just bit9.
>> >>>> >
>> >>>> The extra XOR is made a no-op for the Y-tiled case in the same way
> that
>> >>>> they are both made a no-op in the no-swizzling case. I'll add
> another
>> >>>> comment clarifying that.
>> >>>
>> >>> I don't think that actually works. In the zero-shift case, the first
> XOR
>> >>> produces an all-zero value, you mask to bit 6 (still all-zero) and
> XOR with
>> >>> the original value and get the original back. In the Y-tiled case,
> you
>> >>> compute a ^ (a >> 3) and mask off bit 6. This gives you bit6 ^ bit9
> in the
>> >>> sixth bit and zero everywhere else. When you then XOR that with the
>> >>> original, the two copies of bit6 cancel out and you are left with
> bit9 only.
>> >>>
>> >> Not exactly, in either case the result of the swizzling calculation
>> >> is:
>> >> addr' = addr ^ ((1 << 6) & ((addr >> swz.x) ^ (addr >> swz.y)))
>> >>
>> >> If the surface is Y-tiled, swz.x = 3 and swz.y = 31, which gives:
>> >> addr' = addr ^ ((1 << 6) & ((addr[9] ^ addr[37]) << 6)) =
>> >> addr ^ ((addr[9] ^ 0) << 6) = addr ^ (addr[9] << 6)
>> >>
>> >> I guess I should add another comment here about how the XOR
> instructions
>> >> are NOP-ed out when they're not needed. :)
>> >
>> > Right. I'd missed the fact that the default swizzle was not zero.
>> > Also, it's 0xff, so it's 255, not 31. I'm not sure what addr >> 255
>> > does. Maybe it only takes 5 bits and it's actually 31, but we should
>> > probably use 31 rather than 255.
>>
>> Yeah, I wrote 31 because the actual value used by the hardware is the
>> LSBs of the shift value depending on the execution type -- I.e. 5 bits
>> for UD. We could definitely initialize the swz parameters to 0x1f as
>> well but I used 0xff instead because it would also work for larger
>> offset types, e.g. 64bit in which case the hardware shift instruction
>> would take the lowest 6 bits -- I'm not planning to extend the code
>> above to handle 64-bit offsets anytime soon though.
>
> I don't care too much which we use. However, there should be comments both
> here and where we set the defaults saying why the defeault is 31/0xff.
>
Sure, I'll fix that.
>> > --Jason
>> >
>> >>>> >> + }
>> >>>> >> +
>> >>>> >> + } else {
>> >>>> >> + /* Multiply by the Bpp/stride value. */
>> >>>> >
>> >>>> > I'm still confused as to how addr can have 2 things while dims ==
> 1.
>> >>>> > Does dims specify the per-slice dimension or total dimension? That
>> >>>> > should probably be documented at the top of the function.
>> >>>> >
>> >>>> dims specifies the dimension of the coord argument. addr may still
> have
>> >>>> a non-zero y coordinate because it's the sum of coord and the
>> >>>> two-dimensional offset value specified by surface set-up. 1D texture
>> >>>> slices and levels are laid out in a 2D layout just like the rest, the
>> >>>> offset value specifies where in the 2D miptree the requested 1D image
>> >>>> starts. You may wonder why we pass a 2D offset to the shader
> instead of
>> >>>> just fixing up the surface base memory address to point at the right
>> >>>> slice at offset (0, 0), the answer is that in the general case (i.e.
> not
>> >>>> necessarily 1D) it wouldn't work, because a level may start mid-tile
> and
>> >>>> the result of shifting a tiled surface by less than the tile size is
> in
>> >>>> general not a well-formed tiled surface -- In the 1D case it could
>> >>>> probably be done though because I deliberately disabled tiling for
> those
>> >>>> (36a17f0f9913), but it would require special-casing them in the
> surface
>> >>>> state set-up code and another manual calculation of the base memory
>> >>>> address of the right slice-level of the miptree.
>> >>>>
>> >>>> >> + bld.MUL(offset(addr, bld, 1),
>> >>>> >> + offset(addr, bld, 1), offset(stride, bld,
> 1));
>> >>>> >> + bld.ADD(addr, addr, offset(addr, bld, 1));
>> >>>> >> + bld.MUL(dst, addr, stride);
>> >>>> >> + }
>> >>>> >> +
>> >>>> >> + return dst;
>> >>>> >> + }
>> >>>> >> + }
>> >>>> >> }
>> >>>> >> --
>> >>>> >> 2.4.3
>> >>>> >>
>> >>>> >> _______________________________________________
>> >>>> >> mesa-dev mailing list
>> >>>> >> mesa-dev at lists.freedesktop.org
>> >>>> >> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
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