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v3d: Drop in a bunch of notes about performance improvement opportunities.

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These have all been floating in my head, and while I've thought about
encoding them in issues on gitlab once they're enabled, they also make
sense to just have in the area of the code you'll need to work in.
This commit is contained in:
Eric Anholt
2018-12-14 14:46:48 -08:00
parent 248a7fb392
commit 29927e7524
5 changed files with 74 additions and 2 deletions
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14
src/broadcom/compiler/v3d40_tex.c
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@@ -34,6 +34,9 @@ static void
vir_TMU_WRITE(struct v3d_compile *c, enum v3d_qpu_waddr waddr, struct qreg val,
int *tmu_writes)
{
/* XXX perf: We should figure out how to merge ALU operations
* producing the val with this MOV, when possible.
*/
vir_MOV_dest(c, vir_reg(QFILE_MAGIC, waddr), val);
(*tmu_writes)++;
@@ -147,6 +150,10 @@ v3d40_vir_emit_tex(struct v3d_compile *c, nir_tex_instr *instr)
/* Limit the number of channels returned to both how many the NIR
* instruction writes and how many the instruction could produce.
*
* XXX perf: Can we also limit to the number of channels that are
* actually read by the users of this NIR dest, so that we don't need
* to emit unused LDTMUs?
*/
uint32_t instr_return_channels = nir_tex_instr_dest_size(instr);
if (!p1_unpacked.output_type_32_bit)
@@ -187,6 +194,7 @@ v3d40_vir_emit_tex(struct v3d_compile *c, nir_tex_instr *instr)
p1_packed |= unit << 24;
vir_WRTMUC(c, QUNIFORM_TMU_CONFIG_P0, p0_packed);
/* XXX perf: Can we skip p1 setup for txf ops? */
vir_WRTMUC(c, QUNIFORM_TMU_CONFIG_P1, p1_packed);
if (memcmp(&p2_unpacked, &p2_unpacked_default, sizeof(p2_unpacked)) != 0)
vir_WRTMUC(c, QUNIFORM_CONSTANT, p2_packed);
@@ -226,6 +234,12 @@ v3d40_vir_emit_tex(struct v3d_compile *c, nir_tex_instr *instr)
STATIC_ASSERT(PIPE_SWIZZLE_X == 0);
chan = return_values[i / 2];
/* XXX perf: We should move this unpacking into NIR.
* That would give us exposure of these types to NIR
* optimization, so that (for example) a repacking of
* half-float samples to the half-float render target
* could be eliminated.
*/
if (nir_alu_type_get_base_type(instr->dest_type) ==
nir_type_float) {
enum v3d_qpu_input_unpack unpack;