feat(linux/vulkan): enable RADV low-latency Vulkan Video encoding

[neatnoise]

Description

Mesa RADV Vulkan driver has added a new low-latency Vulkan Video encode option (lowlatencyenc) for AMD VCN GPUs, merged to Mesa Git for the upcoming Mesa 26.1 release. This lowers video encoding latency at the cost of higher GPU power usage.

This PR appends lowlatencyenc to the existing RADV_PERFTEST environment variable, alongside the already-set video_encode flag. This enables low-latency Vulkan Video encoding by default on AMD GPUs using the RADV driver.

The RadeonSI/VA-API path already benefits from the existing AMD_DEBUG=lowlatencyenc that Sunshine sets.

Screenshot

Issues Fixed or Closed

Roadmap Issues

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
• perf: Code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

AI Usage

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Bundle Report

Changes will decrease total bundle size by 784.43kB (-49.96%) ⬇️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
rapideye-esm	(removed)	-784.43kB (-100.0%) ⬇️

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 17.96%. Comparing base (5a41707) to head (354ca6f).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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- Coverage   17.99%   17.96%   -0.03%     
==========================================
  Files         108      108              
  Lines       23424    23424              
  Branches    10340    10340              
==========================================
- Hits         4216     4209       -7     
+ Misses      16242    14236    -2006     
- Partials     2966     4979    +2013     

Flag	Coverage Δ
Archlinux	11.60% <0.00%> (ø)
FreeBSD-14.3-aarch64	?
FreeBSD-14.3-amd64	13.59% <0.00%> (ø)
Homebrew-ubuntu-22.04	13.92% <100.00%> (ø)
Linux-AppImage	12.21% <100.00%> (ø)
Windows-AMD64	14.90% <ø> (ø)
Windows-ARM64	13.22% <ø> (-0.01%)	⬇️
macOS-arm64	19.02% <ø> (ø)
macOS-x86_64	18.39% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/platform/linux/misc.cpp	15.60% <100.00%> (ø)

... and 51 files with indirect coverage changes

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[gschintgen]

Hi, out of curiosity: how does this interact with Sunshine's current Vulkan tuning options? Doesn't this force-override the user-chosen tuning setting?

See for example this discussion: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40524#note_3384466

(I did not actually test the new behaviour, I'm just wondering.)

Thanks for all your other recent work, it's appreciated!

[gschintgen]

Here's the relevant code change on AMD's side: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40524/diffs?commit_id=c1722405d6ea0f5f1a8756683a83a3465771c842&file=46855871bcdc5640eb0b11b0acc8d8eca28398b3#46855871bcdc5640eb0b11b0acc8d8eca28398b3_1080_1080

If I'm reading that correctly the env variable is just an alternative to setting the tuning parameter (which Sunshine already does, AFAIK).

[neatnoise]

@gschintgen good spot. I added condition. Could you @ReenigneArcher please reopen the PR with latest neatnoise:radv-lowlatency-vulkan-video changes?

[ReenigneArcher]

Merged PRs cannot be re-opened.