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sfu: patch pacer header extensions without per-packet allocation - #4872

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sfu: patch pacer header extensions without per-packet allocation#4872
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raja/pacer-ext-no-alloc

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@boks1971 boks1971 commented Sep 15, 2026

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Summary

Base.SendPacket allocated four times for every down track write: a 3 byte slice from AbsSendTimeExtension.Marshal, a 2 byte slice from TransportCCExtension.Marshal, and two append growths because the pooled rtp.Header was reset to a zero value, which dropped its Extensions backing array.

Follow-up to #4871, from the same profiling of a media node hosting a ~250 participant room.

Changes

  • pacer.Packet gets two fixed scratch arrays (absSendTimeBuf [3]byte, twccBuf [2]byte). patchRTPHeaderExtensions marshals into them with MarshalTo and points the header extensions at them. The Packet is pooled and owned by exactly one send until SendPacket returns, so the scratch is never shared between down tracks even though the pacer itself is shared per participant.
  • SendPacket keeps the pooled header's Extensions capacity when returning it to the pool (entries cleared, length zero).
  • New initPooledRTPHeader helper in pkg/sfu keeps that capacity when a down track initializes a pooled header. Used at the four RTPHeaderFactory sites in downtrack.go (media, padding, RTX, blank frames).
  • pacer/base_test.go: asserts zero allocations per SendPacket with both extensions enabled, and that both extensions are present on the written header.

Verification

  • go test ./pkg/sfu/... passes.
  • New test: 0 allocations per SendPacket (was 4).
  • go build -gcflags=-m shows no new escapes on the send path or header init sites.

🤖 Generated with Claude Code

@boks1971 @claude
sfu: patch pacer header extensions without per-packet allocation
6d80a36 
SendPacket allocated four times per down track write: a 3 byte slice for
abs-send-time, a 2 byte slice for transport-cc, and two appends to a nil
Extensions slice because the pooled header was reset to a zero value.

Give pacer.Packet fixed scratch arrays for the two extensions and marshal
into them. The Packet is pooled and owned by one send until SendPacket
returns, so nothing is shared across down tracks. Keep the pooled header's
Extensions capacity across reuse, both when returning it to the pool and
when a down track initializes it.

Adds a test that asserts zero allocations per SendPacket.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
@boks1971
boks1971 requested a review from a team as a code owner September 15, 2026 16:10
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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

Devin Review

@boks1971
boks1971 merged commit 61a31d3 into master Sep 15, 2026
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@boks1971
boks1971 deleted the raja/pacer-ext-no-alloc branch September 15, 2026 16:18
@boks1971 boks1971 mentioned this pull request Sep 15, 2026
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@tsenart tsenart mentioned this pull request Sep 16, 2026
Merged
eleboucher pushed a commit to eleboucher/homelab that referenced this pull request Oct 7, 2026
bot-owl @eleboucher
fix(container): update image docker.io/livekit/livekit-server (v1.13.…
227a429 
…7 ➔ v1.13.8) (#2275)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [docker.io/livekit/livekit-server](https://github.com/livekit/livekit) | patch | `v1.13.7` → `v1.13.8` |

---

### Release Notes

<details>
<summary>livekit/livekit (docker.io/livekit/livekit-server)</summary>

### [`v1.13.8`](https://github.com/livekit/livekit/releases/tag/v1.13.8)

[Compare Source](livekit/livekit@v1.13.7...v1.13.8)

##### Added

- agent: HTTP endpoints data plane ([#&#8203;4779](livekit/livekit#4779))
- use sender report pass through setting to forward abs-capture-time verbatim ([#&#8203;4812](livekit/livekit#4812))
- Add sdk lable to session start time and participant join ([#&#8203;4885](livekit/livekit#4885))
- Add a local participant method to get recently disconnected ([#&#8203;4911](livekit/livekit#4911))
- service: start room composite egress configured in a room preset ([#&#8203;4926](livekit/livekit#4926))

##### Changed

- Update github workflows ([#&#8203;4446](livekit/livekit#4446))
- Reduce descriptor marshal allocations on Go 1.26.4/linux-amd64 ([#&#8203;4681](livekit/livekit#4681))
- config: reject unknown send\_side\_bwe\_pacer, warn on unwired fallback ([#&#8203;4804](livekit/livekit#4804))
- Update github.com/livekit/protocol digest to [`a879e94`](livekit/livekit@a879e94) ([#&#8203;4864](livekit/livekit#4864))
- Update module github.com/gotesttools/gotestfmt/v2 to v2.5.0 ([#&#8203;4865](livekit/livekit#4865))
- Update module github.com/urfave/cli/v3 to v3.11.0 ([#&#8203;4867](livekit/livekit#4867))
- Update module golang.org/x/mod to v0.41.0 ([#&#8203;4868](livekit/livekit#4868))
- sfu: return VP8 munged header by value to avoid per-packet allocation ([#&#8203;4871](livekit/livekit#4871))
- sfu: patch pacer header extensions without per-packet allocation ([#&#8203;4872](livekit/livekit#4872))
- Update pion/sdp to get lesser SDP retention ([#&#8203;4873](livekit/livekit#4873))
- sfu: skip pacer allocation assertion under the race detector ([#&#8203;4874](livekit/livekit#4874))
- sfu: broadcast RTP to down tracks without per-packet allocations ([#&#8203;4875](livekit/livekit#4875))
- Track action versions and stop quarantining our own actions ([#&#8203;4877](livekit/livekit#4877))
- test: fix two data races in the test suites ([#&#8203;4878](livekit/livekit#4878))
- Bump go.opentelemetry.io/otel/sdk ([#&#8203;4879](livekit/livekit#4879))
- deps: update psrpc to v0.8.0 ([#&#8203;4882](livekit/livekit#4882))
- Update module github.com/moby/moby/client to v0.6.0 ([#&#8203;4883](livekit/livekit#4883))
- Update module golang.org/x/sync to v0.23.0 ([#&#8203;4884](livekit/livekit#4884))
- Propagate SIP\_TRUNK\_FAILURE ([#&#8203;4890](livekit/livekit#4890))
- ccutils: use millisecond resolution for probe interval backoff ([#&#8203;4891](livekit/livekit#4891))
- Increase receiver loadbalance threshold when batch io enabled ([#&#8203;4899](livekit/livekit#4899))
- rtc: parse each remote offer once per negotiation ([#&#8203;4904](livekit/livekit#4904))
- Bump protocol ([#&#8203;4909](livekit/livekit#4909))
- rtc: split EndSession out of MoveToRoom ([#&#8203;4917](livekit/livekit#4917))
- telemetry: drop the stats worker re-key path ([#&#8203;4918](livekit/livekit#4918))
- sfu: report forwarding latency as p90 instead of the mean ([#&#8203;4920](livekit/livekit#4920))
- rtc: accept ICE Completed in ICE-restart connect assertions ([#&#8203;4921](livekit/livekit#4921))
- rtc: measure data blob keys by their content, not their text form ([#&#8203;4923](livekit/livekit#4923))
- Remove deprecatred way of setting prometheus from the config file ([#&#8203;4928](livekit/livekit#4928))
- test: give mock participants a connection quality, close test rooms ([#&#8203;4933](livekit/livekit#4933))
- update warp dep ([#&#8203;4943](livekit/livekit#4943))

##### Fixed

- Do not add down tracks after receiver close ([#&#8203;4857](livekit/livekit#4857))
- Do not request media sections for transceivers that cannot send ([#&#8203;4892](livekit/livekit#4892))
- Deregister agent job when the server terminates it ([#&#8203;4893](livekit/livekit#4893))
- sfu: don't hold bindLock across the blank-frame flush in CloseWithFlush ([#&#8203;4895](livekit/livekit#4895))
- dynacast: re-send subscribed qualities after every publisher answer ([#&#8203;4907](livekit/livekit#4907))
- agent: release JobTerminate handler when job ends before registration ([#&#8203;4908](livekit/livekit#4908))
- Report disconnected for older disconnected participants. ([#&#8203;4910](livekit/livekit#4910))
- rtc: record a room's departure when the participant leaves it ([#&#8203;4913](livekit/livekit#4913))
- update deps to fix warp issue ([#&#8203;4916](livekit/livekit#4916))
- sfu: fix data stats active window bitrate and duration units ([#&#8203;4922](livekit/livekit#4922))
- fix: reject instead of drop for no dispatch rule ([#&#8203;4927](livekit/livekit#4927))
- fix: skip RTX/FEC when picking a fallback video codec ([#&#8203;4930](livekit/livekit#4930))
- fix: do not read invalid delta ([#&#8203;4935](livekit/livekit#4935))
- fix: use the fast debounce for the first negotiation ([#&#8203;4936](livekit/livekit#4936))
- fix: skip DTLS HelloVerifyRequest ([#&#8203;4937](livekit/livekit#4937))
- config: parse generated duration flags as durations ([#&#8203;4939](livekit/livekit#4939))
- fix: use the most common recent packet rate in connection quality ([#&#8203;4940](livekit/livekit#4940))
- fix: copy RED history packets instead of keeping pointers ([#&#8203;4941](livekit/livekit#4941))
- fix: keep one subscription when first subscribes race ([#&#8203;4944](livekit/livekit#4944))
- bump protocol to get unlock on no key fix ([#&#8203;4945](livekit/livekit#4945))
- fix: count leftover upstream loss after RTX repairs ([#&#8203;4946](livekit/livekit#4946))
- fix: switch VP8 temporal layer up only at a layer sync frame ([#&#8203;4947](livekit/livekit#4947))
- fix: reconcile everything when the reconcile queue overflows ([#&#8203;4948](livekit/livekit#4948))
- fix: enable H.264 publish for desktop Linux Firefox ([#&#8203;4949](livekit/livekit#4949))

</details>

---

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This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0NC4xMzMuMCIsInVwZGF0ZWRJblZlciI6IjQ0LjEzMy4wIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->

Reviewed-on: https://git.erwanleboucher.dev/eleboucher/homelab/pulls/2275
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