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radeonsi: optimize out LDS bank conflicts in the NGG culling shader 

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7172>
This commit is contained in:
Marek Olšák 2020-10-15 08:10:46 -04:00 committed by Marge Bot
parent 7648060dc0
commit 823ee12d57
1 changed files with 27 additions and 7 deletions
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34
src/gallium/drivers/radeonsi/gfx10_shader_ngg.c
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@ -649,20 +649,41 @@ static LLVMValueRef si_insert_input_v4i32(struct si_shader_context *ctx, LLVMVal
}
static void load_bitmasks_2x64(struct si_shader_context *ctx, LLVMValueRef lds_ptr,
unsigned dw_offset, LLVMValueRef mask[2],
LLVMValueRef tid,
unsigned dw_offset, LLVMValueRef mask[4],
LLVMValueRef *total_bitcount)
{
LLVMBuilderRef builder = ctx->ac.builder;
LLVMValueRef ptr64 = LLVMBuildPointerCast(
builder, lds_ptr, LLVMPointerType(LLVMArrayType(ctx->ac.i64, 2), AC_ADDR_SPACE_LDS), "");
LLVMValueRef tmp[2];
for (unsigned i = 0; i < 2; i++)
tmp[i] = ac_build_alloca_undef(&ctx->ac, ctx->ac.i64, "");
/* If all threads loaded the bitmasks, it would cause many LDS bank conflicts
* and the performance could decrease up to WaveSize times (32x or 64x).
*
* Therefore, only load the bitmasks in thread 0 and other threads will get them
* through readlane.
*/
ac_build_ifcc(&ctx->ac, LLVMBuildICmp(builder, LLVMIntEQ, tid, ctx->ac.i32_0, ""), 17771);
for (unsigned i = 0; i < 2; i++) {
LLVMValueRef index = LLVMConstInt(ctx->ac.i32, dw_offset / 2 + i, 0);
mask[i] = LLVMBuildLoad(builder, ac_build_gep0(&ctx->ac, ptr64, index), "");
LLVMValueRef val = LLVMBuildLoad(builder, ac_build_gep0(&ctx->ac, ptr64, index), "");
LLVMBuildStore(builder, val, tmp[i]);
}
ac_build_endif(&ctx->ac, 17771);
/* We get better code if we don't use the 128-bit bitcount. */
*total_bitcount = LLVMBuildAdd(builder, ac_build_bit_count(&ctx->ac, mask[0]),
ac_build_bit_count(&ctx->ac, mask[1]), "");
*total_bitcount = ctx->ac.i32_0;
for (unsigned i = 0; i < 2; i++) {
tmp[i] = LLVMBuildLoad(builder, tmp[i], "");
mask[i] = ac_build_readlane_no_opt_barrier(&ctx->ac, tmp[i], NULL);
*total_bitcount = LLVMBuildAdd(builder, *total_bitcount,
ac_build_bit_count(&ctx->ac, mask[i]), "");
}
}
/**
@ -969,8 +990,7 @@ void gfx10_emit_ngg_culling_epilogue(struct ac_shader_abi *abi, unsigned max_out
/* Load the vertex masks and compute the new ES thread count. */
LLVMValueRef es_mask[2], new_num_es_threads, kill_wave;
load_bitmasks_2x64(ctx, ngg_scratch, 0, es_mask, &new_num_es_threads);
new_num_es_threads = ac_build_readlane_no_opt_barrier(&ctx->ac, new_num_es_threads, NULL);
load_bitmasks_2x64(ctx, ngg_scratch, tid, 0, es_mask, &new_num_es_threads);
/* ES threads compute their prefix sum, which is the new ES thread ID.
* Then they write the value of the old thread ID into the LDS address