PR #21067 opened by averne URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21067 Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21067.patch
This introduces a small per-invocation buffer in shared memory, to store bitstream data and decrease the number of global memory reads. The bitstream read head is first aligned to a 4-byte boundary, so that we can use u32vec4 to perform the read. On architectures that support it (AMD/NV, don't know about others), that compiles to a single instruction. It can probably be used in other VK-based decoders, with minimal modifications. On the ProRes decoder, I measured the following speedup (5760x3040 422p10, 3840x2160 422p10): NVIDIA 3050: 65%, 87% AMD 6700XT: 16%, 22% Intel Tiger Lake GT2: 6%, 4% >From ef7354d471c18ec5c998220eaa4a95bdd36ccb6a Mon Sep 17 00:00:00 2001 From: averne <[email protected]> Date: Sat, 29 Nov 2025 22:33:26 +0100 Subject: [PATCH 1/3] libavcodec/vulkan: introduce cached bitstream reader This stores a small buffer in shared memory per decode thread (16 bytes), which helps reduce the number of memory accesses. The bitstream buffer is first aligned to a 4 byte boundary, so that the buffer can be filled with a single memory request. --- libavcodec/vulkan/common.comp | 42 +++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/libavcodec/vulkan/common.comp b/libavcodec/vulkan/common.comp index eda92ce28d..4b71dfd2f4 100644 --- a/libavcodec/vulkan/common.comp +++ b/libavcodec/vulkan/common.comp @@ -42,6 +42,10 @@ layout(buffer_reference, buffer_reference_align = 4) buffer u32vec2buf { u32vec2 v; }; +layout(buffer_reference, buffer_reference_align = 4) buffer u32vec4buf { + u32vec4 v; +}; + layout(buffer_reference, buffer_reference_align = 8) buffer u64buf { uint64_t v; }; @@ -198,8 +202,12 @@ struct GetBitContext { uint64_t bits; int bits_valid; int size_in_bits; +#ifdef GET_BITS_SMEM + int cur_smem_pos; +#endif }; +#ifndef GET_BITS_SMEM #define LOAD64() \ { \ u8vec4buf ptr = u8vec4buf(gb.buf); \ @@ -218,6 +226,40 @@ struct GetBitContext { gb.bits = uint64_t(rf) << (32 - gb.bits_valid) | gb.bits; \ gb.bits_valid += 32; \ } +#else /* GET_BITS_SMEM */ +shared u32vec4 gb_storage[gl_WorkGroupSize.x*gl_WorkGroupSize.y*gl_WorkGroupSize.z]; + +#define FILL_SMEM() \ + { \ + u32vec4buf ptr = u32vec4buf(gb.buf); \ + gb_storage[gl_LocalInvocationIndex] = ptr[0].v; \ + gb.cur_smem_pos = 0; \ + } + +#define LOAD64() \ + { \ + gb.bits = 0; \ + gb.bits_valid = 0; \ + u8buf ptr = u8buf(gb.buf); \ + for (uint i = 0; i < ((4 - uint(gb.buf_start)) & 3); ++i) { \ + gb.bits |= uint64_t(ptr[i].v) << (56 - i * 8); \ + gb.bits_valid += 8; \ + gb.buf += 1; \ + } \ + FILL_SMEM(); \ + } + +#define RELOAD32() \ + { \ + if (gb.cur_smem_pos >= 4) \ + FILL_SMEM(); \ + uint v = gb_storage[gl_LocalInvocationIndex][gb.cur_smem_pos]; \ + gb.buf += 4; \ + gb.bits = uint64_t(reverse4(v)) << (32 - gb.bits_valid) | gb.bits; \ + gb.bits_valid += 32; \ + gb.cur_smem_pos += 1; \ + } +#endif /* GET_BITS_SMEM */ void init_get_bits(inout GetBitContext gb, u8buf data, int len) { -- 2.49.1 >From fd2fd3828c1e7384d06afee7481d61865ab6cfa7 Mon Sep 17 00:00:00 2001 From: averne <[email protected]> Date: Sun, 30 Nov 2025 13:25:37 +0100 Subject: [PATCH 2/3] libavcodec/vulkan: remove unnessary member in GetBitContext The number of remaining bits can be calculated using existing state. This simplifies calculations and frees up one register. --- libavcodec/vulkan/common.comp | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/libavcodec/vulkan/common.comp b/libavcodec/vulkan/common.comp index 4b71dfd2f4..f5f466ce31 100644 --- a/libavcodec/vulkan/common.comp +++ b/libavcodec/vulkan/common.comp @@ -201,7 +201,6 @@ struct GetBitContext { uint64_t bits; int bits_valid; - int size_in_bits; #ifdef GET_BITS_SMEM int cur_smem_pos; #endif @@ -265,7 +264,6 @@ void init_get_bits(inout GetBitContext gb, u8buf data, int len) { gb.buf = gb.buf_start = uint64_t(data); gb.buf_end = uint64_t(data) + len; - gb.size_in_bits = len * 8; /* Preload */ LOAD64() @@ -320,5 +318,5 @@ int tell_bits(in GetBitContext gb) int left_bits(in GetBitContext gb) { - return gb.size_in_bits - int(gb.buf - gb.buf_start) * 8 + gb.bits_valid; + return int(gb.buf_end - gb.buf) * 8 + gb.bits_valid; } -- 2.49.1 >From 9d65c4af8baf8a8c35d7f1eb3b3ddb3d2d46cc59 Mon Sep 17 00:00:00 2001 From: averne <[email protected]> Date: Sat, 29 Nov 2025 22:33:45 +0100 Subject: [PATCH 3/3] vulkan/prores: use cached bitstream reader when possible Check for sanity that the hardware is capable of holding the required data in shared memory. Speedup is around 25%. --- libavcodec/vulkan_prores.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/libavcodec/vulkan_prores.c b/libavcodec/vulkan_prores.c index 0c704c3d1c..b945ab9c38 100644 --- a/libavcodec/vulkan_prores.c +++ b/libavcodec/vulkan_prores.c @@ -21,7 +21,6 @@ #include "hwaccel_internal.h" #include "libavutil/mem.h" #include "libavutil/vulkan.h" -#include "libavutil/vulkan_loader.h" #include "libavutil/vulkan_spirv.h" extern const char *ff_source_common_comp; @@ -207,14 +206,12 @@ static int vk_prores_end_frame(AVCodecContext *avctx) RET(ff_vk_exec_mirror_sem_value(&ctx->s, exec, &vp->sem, &vp->sem_value, pr->frame)); + /* Transfer ownership to the exec context */ RET(ff_vk_exec_add_dep_buf(&ctx->s, exec, &vp->slices_buf, 1, 0)); vp->slices_buf = NULL; RET(ff_vk_exec_add_dep_buf(&ctx->s, exec, &pp->metadata_buf, 1, 0)); pp->metadata_buf = NULL; - /* Transfer ownership to the exec context */ - vp->slices_buf = pp->metadata_buf = NULL; - /* Input barrier */ ff_vk_frame_barrier(&ctx->s, exec, pr->frame, img_bar, &nb_img_bar, VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT, @@ -390,7 +387,7 @@ static int init_shader(AVCodecContext *avctx, FFVulkanContext *s, FFVkExecPool *pool, FFVkSPIRVCompiler *spv, FFVulkanShader *shd, const char *name, const char *entrypoint, FFVulkanDescriptorSetBinding *descs, int num_descs, - const char *source, int local_size, int interlaced) + const char *source, int local_size, int interlaced, int gb_smem) { uint8_t *spv_data; size_t spv_len; @@ -404,6 +401,12 @@ static int init_shader(AVCodecContext *avctx, FFVulkanContext *s, local_size >> 16 & 0xff, local_size >> 8 & 0xff, local_size >> 0 & 0xff, 0)); + if (gb_smem) + av_bprintf(&shd->src, "#define GET_BITS_SMEM\n"); + + if (interlaced) + av_bprintf(&shd->src, "#define INTERLACED\n"); + /* Common code */ GLSLD(ff_source_common_comp); @@ -412,9 +415,6 @@ static int init_shader(AVCodecContext *avctx, FFVulkanContext *s, RET(ff_vk_shader_add_descriptor_set(s, shd, descs, num_descs, 0, 0)); - if (interlaced) - av_bprintf(&shd->src, "#define INTERLACED\n"); - /* Main code */ GLSLD(source); @@ -493,7 +493,8 @@ static int vk_decode_prores_init(AVCodecContext *avctx) }; RET(init_shader(avctx, &ctx->s, &ctx->exec_pool, spv, &pv->reset, "prores_dec_reset", "main", desc_set, 1, - ff_source_prores_reset_comp, 0x080801, pr->frame_type != 0)); + ff_source_prores_reset_comp, 0x080801, pr->frame_type != 0, 0)); + desc_set = (FFVulkanDescriptorSetBinding []) { { .name = "slice_offsets_buf", @@ -524,7 +525,8 @@ static int vk_decode_prores_init(AVCodecContext *avctx) }; RET(init_shader(avctx, &ctx->s, &ctx->exec_pool, spv, &pv->vld, "prores_dec_vld", "main", desc_set, 3, - ff_source_prores_vld_comp, 0x080801, pr->frame_type != 0)); + ff_source_prores_vld_comp, 0x080801, pr->frame_type != 0, + ctx->s.props.properties.limits.maxComputeSharedMemorySize >= 64*16)); desc_set = (FFVulkanDescriptorSetBinding []) { { @@ -547,7 +549,7 @@ static int vk_decode_prores_init(AVCodecContext *avctx) }; RET(init_shader(avctx, &ctx->s, &ctx->exec_pool, spv, &pv->idct, "prores_dec_idct", "main", desc_set, 2, - ff_source_prores_idct_comp, 0x200201, pr->frame_type != 0)); + ff_source_prores_idct_comp, 0x200201, pr->frame_type != 0, 0)); err = 0; -- 2.49.1 _______________________________________________ ffmpeg-devel mailing list -- [email protected] To unsubscribe send an email to [email protected]
