[WebGPU] Improve GPUBindGroup performance using one device-shared argument MTLBuffer

• Component: New Bugs
• Status: RESOLVED FIXED

[Justin Fan]

[WebGPU] Improve GPUBindGroup performance using one device-shared argument MTLBuffer

[Justin Fan]

Created attachment 375999 [details]
Patch

[Myles C. Maxfield]

Comment on attachment 375999 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=375999&action=review

> Source/WebCore/ChangeLog:9
> +        Vastly improves GPUProgrammablePassEncoder.setBindGroup performance.

By how much? On which benchmark?

[Myles C. Maxfield]

Justin and I had a long conversation this morning about allocation strategies. We should do some more investigation to determine whether the strategy in this patch is acceptable to commit or not.

[Justin Fan]

Created attachment 376087 [details]
Patch

[Justin Fan]

Created attachment 376106 [details]
Patch

[Justin Fan]

Talked with Geoff Garen about memory allocation strategies. A vector-like growth model with a minimum size should be fine for now, especially since it appears that shared MTLBuffers have a minimum allocation size (4KB on a tested Mac) way larger than the average argument buffer.

For future, we should free unused argument buffer memory. This requires:
1) Compaction logic before deciding whether to allocate new memory for a new GPUBindGroup, and
2) Defragmentation logic whenever a GPUBindGroup is released. 

I'll file bugs to address these two issues.

[Justin Fan]

To back up my "average argument buffer" size claim, here are some numbers:

Tier 1 Argument Buffer support in Metal on iOS devices is the minimum. Each argument buffer can encode:

31 buffers, which require 32 bytes each (16 bytes for pointer and 16 bytes for size constant)
31 textures, which require 32 bytes each
16 samplers, which require 16 bytes each

And other than the constant data we encode for buffer bounds checking, we don't support encoding extra constant data.

This means each argument buffer we support has a maximum possible encodedLength of 2240 B. A GPUBindGroup uses one argument buffer per pipeline stage type, so for the three of vertex, fragment, and compute, worst case argument buffer size for a single GPUBindGroup is 6720 B.

[Myles C. Maxfield]

Comment on attachment 376106 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=376106&action=review

r=me assuming there are links to follow-up bugs about compaction and shrinking.

> Source/WebCore/platform/graphics/gpu/cocoa/GPUBindGroupAllocatorMetal.mm:83
> +        // Based off mimimum allocation for a memory-shared MTLBuffer on macOS.

don't you mean "shared memory"

> Source/WebCore/platform/graphics/gpu/cocoa/GPUBindGroupAllocatorMetal.mm:127
> +

Seems like this could benefit from a FIXME with a link to a bug about compaction

[Justin Fan]

Created attachment 376137 [details]
Patch for landing

[Justin Fan]

Filed https://bugs.webkit.org/show_bug.cgi?id=200658 and https://bugs.webkit.org/show_bug.cgi?id=200657

[WebKit Commit Bot]

Comment on attachment 376137 [details]
Patch for landing

Rejecting attachment 376137 [details] from commit-queue.

Failed to run "['/Volumes/Data/EWS/WebKit/Tools/Scripts/webkit-patch', '--status-host=webkit-queues.webkit.org', '--bot-id=webkit-cq-03', 'apply-attachment', '--no-update', '--non-interactive', 376137, '--port=mac']" exit_code: 2 cwd: /Volumes/Data/EWS/WebKit

Logging in as [e-mail]...
Fetching: https://bugs.webkit.org/attachment.cgi?id=376137&action=edit
Fetching: https://bugs.webkit.org/show_bug.cgi?id=200606&ctype=xml&excludefield=attachmentdata
Processing 1 patch from 1 bug.
Processing patch 376137 from bug 200606.
Fetching: https://bugs.webkit.org/attachment.cgi?id=376137
Failed to run "[u'/Volumes/Data/EWS/WebKit/Tools/Scripts/svn-apply', '--force']" exit_code: 1 cwd: /Volumes/Data/EWS/WebKit

Parsed 25 diffs from patch file(s).
patching file Source/WebCore/ChangeLog
Hunk #1 succeeded at 1 with fuzz 3.
patching file Source/WebCore/Modules/webgpu/WebGPUDevice.cpp
patching file Source/WebCore/SourcesCocoa.txt
patching file Source/WebCore/WebCore.xcodeproj/project.pbxproj
Hunk #1 succeeded at 13934 (offset 2 lines).
Hunk #2 FAILED at 17088.
Hunk #3 succeeded at 18275 (offset 2 lines).
Hunk #4 succeeded at 26066 (offset 4 lines).
Hunk #5 succeeded at 28609 (offset 4 lines).
Hunk #6 succeeded at 30824 (offset 4 lines).
1 out of 6 hunks FAILED -- saving rejects to file Source/WebCore/WebCore.xcodeproj/project.pbxproj.rej
patching file Source/WebCore/platform/graphics/gpu/GPUBindGroup.h
patching file Source/WebCore/platform/graphics/gpu/GPUBindGroupAllocator.h
patching file Source/WebCore/platform/graphics/gpu/GPUBindGroupLayout.h
patching file Source/WebCore/platform/graphics/gpu/GPUBuffer.h
patching file Source/WebCore/platform/graphics/gpu/GPUComputePassEncoder.h
patching file Source/WebCore/platform/graphics/gpu/GPUDevice.cpp
patching file Source/WebCore/platform/graphics/gpu/GPUDevice.h
patching file Source/WebCore/platform/graphics/gpu/GPUProgrammablePassEncoder.h
patching file Source/WebCore/platform/graphics/gpu/GPURenderPassEncoder.h
patching file Source/WebCore/platform/graphics/gpu/GPUTexture.h
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUBindGroupAllocatorMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUBindGroupMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUBufferMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUComputePassEncoderMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUDeviceMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUProgrammablePassEncoderMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPURenderPassEncoderMetal.mm
patching file Source/WebCore/platform/graphics/gpu/cocoa/GPUTextureMetal.mm
patching file LayoutTests/ChangeLog
Hunk #1 succeeded at 1 with fuzz 3.
patching file LayoutTests/webgpu/bind-groups-expected.txt
patching file LayoutTests/webgpu/bind-groups.html

Failed to run "[u'/Volumes/Data/EWS/WebKit/Tools/Scripts/svn-apply', '--force']" exit_code: 1 cwd: /Volumes/Data/EWS/WebKit

Full output: https://webkit-queues.webkit.org/results/12905201

[Justin Fan]

Created attachment 376203 [details]
Patch

[Justin Fan]

Comment on attachment 376203 [details]
Patch

Clearing flags on attachment: 376203

Committed r248606: <https://trac.webkit.org/changeset/248606>

[Justin Fan]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/54269779>

[Justin Fan]

*** Bug 198683 has been marked as a duplicate of this bug. ***