Raspberry Pi 3 B+: Wi-Fi latency regression on 6.18.39+rpt-rpi-v8; 6.18.33 works

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Đánh giá

Độ khó
4/5
Thời gian dự kiến
3-5 ngày
Mức phù hợp với người mới
45/100
Loại issue
Lỗi
Độ rõ ràng
Khá rõ ràng
Mức độ hoạt động
Sôi nổi
Công nghệ
c, linux, raspberry-pi
Lĩnh vực
embedded-iot, networking, operating-systems

Hướng nghiên cứu

Start by reproducing the gateway-ping comparison on the Raspberry Pi 3 B+ with kernels 6.18.39+rpt-rpi-v8 and 6.18.33+rpt-rpi-v8, using the onboard brcmfmac adapter and the reported power-saving settings. Then investigate the kernel changes between those versions; done means identifying and correcting the regression while preserving normal latency on the affected setup.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.

Mô tả

Describe the bug

After upgrading a Raspberry Pi 3 Model B+ from 6.18.33+rpt-rpi-v8 to 6.18.39+rpt-rpi-v8, onboard Wi-Fi exhibits a repeating latency pattern: most gateway pings take approximately 105–113 ms, interspersed with normal 4–8 ms responses.

There is no packet loss, signal strength is excellent, the system is idle, and Wi-Fi power saving is disabled.

Booting the same system into the retained 6.18.33+rpt-rpi-v8 kernel restores normal latency. No firmware, userspace, NetworkManager, access-point, or Wi-Fi profile changes were made between the decisive tests.

Results

6.18.39+rpt-rpi-v8, Wi-Fi only:

10 packets transmitted, 10 received, 0% packet loss
rtt min/avg/max/mdev = 5.360/78.668/112.640/47.331 ms

Representative responses:

107 ms
110 ms
5.36 ms
111 ms
112 ms
8.63 ms
105 ms
113 ms
5.40 ms
110 ms

6.18.33+rpt-rpi-v8, Wi-Fi only:

20 packets transmitted, 20 received, 0% packet loss
rtt min/avg/max/mdev = 2.110/6.990/39.653/7.566 ms

Apart from one 39.7 ms response, replies were normally 4–6 ms.

The working 6.18.33 test was performed on the same 5 GHz AP radio and frequency (5500 MHz) used when the problem was initially observed.

Steps to reproduce the behaviour

  1. Use a Raspberry Pi 3 Model B+ running 64-bit Debian 13 / Raspberry Pi OS Lite.
  2. Install and boot linux-image-6.18.39+rpt-rpi-v8.
  3. Connect using the onboard BCM4345/6 Wi-Fi adapter.
  4. Disable Wi-Fi power saving.
  5. Disconnect Ethernet.
  6. Run ping -c 20 <LAN gateway>.
  7. Observe repeating responses around 105–113 ms with periodic normal responses.
  8. Boot the same system into linux-image-6.18.33+rpt-rpi-v8, without changing the Wi-Fi firmware or configuration.
  9. Repeat the ping test.
  10. Observe normal latency around 4–6 ms.

Device(s)

Raspberry Pi 3 Mod. B+

System

Raspberry Pi reference 2026-04-21
Generated using pi-gen:
4ad56cc850fa60adcc7f07dc15879bc95cc1d281
stage2

Debian GNU/Linux 13.6 (trixie)
aarch64

Affected kernel:

Linux 6.18.39+rpt-rpi-v8
#1 SMP PREEMPT Debian 1:6.18.39-1+rpt1 (2026-07-29)

Working kernel:

Linux 6.18.33+rpt-rpi-v8
#1 SMP PREEMPT Debian 1:6.18.33-1+rpt1 (2026-06-01)

Firmware:

May 21 2026 11:21:57
version 288930ab4712b99596f32732664aaaeb881ef1e0

Relevant packages:

firmware-brcm80211 1:20260519-1~bpo13+1+rpt1
linux-image-6.18.33+rpt-rpi-v8 1:6.18.33-1+rpt1
linux-image-6.18.39+rpt-rpi-v8 1:6.18.39-1+rpt1
network-manager 1.52.1-1+rpt4
wireless-regdb 2026.05.30-1~deb13u1
wpasupplicant 2:2.10-24

Wi-Fi chipset and firmware:

brcmfmac: using brcm/brcmfmac43455-sdio for chip BCM4345/6
brcmfmac: Firmware: BCM4345/6 wl0: Aug 29 2023 01:47:08
version 7.45.265 (28bca26 CY)
FWID 01-b677b91b

Logs

On the working kernel, NetworkManager briefly enables power saving during initialization and then disables it as configured:

brcmfmac: brcmf_cfg80211_set_power_mgmt: power save enabled
brcmfmac: brcmf_cfg80211_set_power_mgmt: power save disabled

Both the global NetworkManager setting and active connection profile specify disabled power saving:

[connection]
wifi.powersave = 2

802-11-wireless.powersave: 2 (disable)

No brcmfmac errors, disconnects, thermal throttling, or packet loss were observed.

Additional context

The upgrade that introduced the problem changed the kernel from 6.18.33 to 6.18.39. It also updated firmware-brcm80211, but the controlled old/new kernel comparison used the same currently installed firmware package, isolating the kernel version as the changed variable.

The latency was reproduced on two different 5 GHz AP radios/channels. Signal strength was reported between 69% and 97%, including approximately -22 dBm near the access point.

This may be related generally to recent Pi 3 brcmfmac regressions, although the symptoms differ from #7337:

https://github.com/raspberrypi/linux/issues/7337

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