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vulkan_prores: pick the bitstream prefetch depth per device

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Same situation as ProRes RAW: with the packet host-mapped, the VLD is
bound by fetch latency over the bus.

Make GET_BITS_SMEM a specialization constant: 32 lines per invocation
on discrete GPUs reading host-mapped packets, 4 otherwise. The 8x8
workgroup makes that 32 KB of shared memory; 64 does not fit, and 40
or 48 measured slower. An integrated GPU loses a third of its speed at
32, so it keeps 4. The depth is clamped to maxComputeSharedMemorySize
for 32 KB devices such as MoltenVK.

5.7K ProRes HQ on an RX 6900 XT: 85 -> 120 fps, bit-identical output.
This commit is contained in:
Lynne
2026-09-20 17:30:24 +09:00
parent 1b5041c785
commit 7d3ace8cb2
2 changed files with 15 additions and 2 deletions
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4
libavcodec/vulkan/prores_vld.comp.glsl
View File

@@ -19,7 +19,9 @@
#pragma shader_stage(compute)
#extension GL_GOOGLE_include_directive : require
#define GET_BITS_SMEM 4
/* Bitstream prefetch depth in 16-byte lines, set by the host */
layout (constant_id = 1) const uint smem_lines = 4;
#define GET_BITS_SMEM smem_lines
#include "common.glsl"
layout (constant_id = 0) const bool interlaced = false;

13
libavcodec/vulkan_prores.c
View File

@@ -374,8 +374,19 @@ static int init_decode_shader(AVCodecContext *avctx, FFVulkanContext *s,
AVHWFramesContext *dec_frames_ctx;
dec_frames_ctx = (AVHWFramesContext *)avctx->hw_frames_ctx->data;
SPEC_LIST_CREATE(sl, 1, 1*sizeof(uint32_t))
/* Discrete GPUs read host-mapped packets over the bus; prefetch more
* to hide the latency. 32 lines (32 KB for the 8x8 workgroup) measured
* best; integrated GPUs get slower with every extra line. Clamp to the
* shared memory limit, leaving 1 KB for the tables. */
int smem_lines = 4;
if (s->props.properties.deviceType == VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU &&
(s->extensions & FF_VK_EXT_EXTERNAL_HOST_MEMORY)) {
uint32_t max_smem = s->props.properties.limits.maxComputeSharedMemorySize;
smem_lines = FFMIN(32, (max_smem - 1024) / (8*8*16));
}
SPEC_LIST_CREATE(sl, 2, 2*sizeof(uint32_t))
SPEC_LIST_ADD(sl, 0, 32, interlaced);
SPEC_LIST_ADD(sl, 1, 32, smem_lines);
ff_vk_shader_load(shd,
VK_SHADER_STAGE_COMPUTE_BIT, sl,