Intel Corporation Comet Lake PCH CNVi WiFi - Linux ~100ms lateny spikes?

[dave_Int_Comm]

G'day,

Summary

The linux support ( Ubuntu LTS 22.04.3 ) for "Intel Corporation Comet Lake PCH CNVi WiFi" has latency spikes of ~100ms every ~10-15 seconds

More details

I have been having small issues with video meetings and started to investigate.

To investigate, I have been doing "ping google.com" and found that the typical ping time is ~15-20ms, but then there are latency spikes of ~100ms every ~10-15 seconds.

After focusing on my internal network, by taking packet captures to see if latency was somewhere in my LAN, I ruled this out.  One big hit is other devices on the my LAN don't see the same latency spikes, so it was only my laptop.

Ultimately I got a MediaTek USB wifi adapter and the spikes are gone. 

The laptop machine is in the same physical location, with the same wifi network, so the difference is the wifi controller and the driver.  The USB device does have large external antennas.

Charts of the Intel wifi latency spikes:

github.com/randomizedcoder/pingTimes/blob/main/intel_wifi_latency_chart_2024-03-11_09-24.png

Data:

github.com/randomizedcoder/pingTimes/blob/main/ping_google.com_2024_03_04.tsv

Charts of new MediaTek:

github.com/randomizedcoder/pingTimes/blob/main/mediatek_wifi_latency_chart_2024-03-11_09-24.png

Data:

github.com/randomizedcoder/pingTimes/blob/main/ping_google.com_2024_03_10_new_usb_wifi.tsv

This adapter has ~100ms latency spikes

lspci | grep -i wifi
00:14.3 Network controller: Intel Corporation Comet Lake PCH CNVi WiFi

ethtool --driver wlp0s20f3
driver: iwlwifi
version: 6.5.0-21-generic
firmware-version: 77.2df8986f.0 QuZ-a0-hr-b0-77.u
expansion-rom-version:
bus-info: 0000:00:14.3
supports-statistics: yes
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi

This is the new USB adapter
lsusb | grep -i wireless
Bus 002 Device 008: ID 0e8d:7612 MediaTek Inc. MT7612U 802.11a/b/g/n/ac Wireless Adapter

ethtool --driver wlp0s20f3
driver: iwlwifi
version: 6.5.0-21-generic
firmware-version: 77.2df8986f.0 QuZ-a0-hr-b0-77.u
expansion-rom-version:
bus-info: 0000:00:14.3
supports-statistics: yes
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no
root@t:/home/das/Downloads/pingTimes# ethtool --driver wlx00c0cab4ac6f
driver: mt76x2u
version: 6.5.0-21-generic
firmware-version: 0.0.00-b1
expansion-rom-version:
bus-info: 2-6:1.0
supports-statistics: yes
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

I would be interested to know if other users are having the same issues. 

I'd love to know what the Intel driver developer thinks.

Thanks in advance,

Dave

[그래요ITech]

Hey Dave

This issue seems to be related to the iwlwifi driver, which is known to cause latency problems in some cases. The MediaTek MT7612U adapter, on the other hand, is showing stable performance, likely due to its different driver and hardware design. 

Here are a few steps you could consider to potentially resolve the issue with the Intel adapter:

1. Update Your System and Drivers: Ensure your system is up-to-date with the latest updates and kernel patches.

• Check for any available updates for the iwlwifi driver that might address this issue.

2. Check Power Management Settings: Sometimes, power-saving features can interfere with network performance. You can try disabling power management for the WiFi adapter to see if it improves the situation.

3. Adjust WiFi Transmission Power: Lowering the transmission power of the WiFi adapter can sometimes reduce interference and improve stability.

4. Change WiFi Channels: Interference from other networks can cause latency spikes. Try switching to a less crowded WiFi channel.

If the problem persists, consider reporting it to the developers of the iwlwifi driver, providing them with all the necessary details and data you've collected.

It's also worth noting that external antennas on USB adapters like the MediaTek MT7612U can significantly improve signal quality and stability, which might explain why you're not seeing the same latency spikes with this adapter.

Hope this helps,

Cheers,

Max

[dave_Int_Comm]

Just an update for others searching.

Pinning the IRQs helps a lot.  Pinning the IRQs to core0, and moving other things away from core 0, brings the max latency down to ~30ms.

Pin IRQs via:

#!/usr/bin/bash

for i in {168..183}
do
echo "Loop:" $i
echo "echo 1 > /proc/irq/${i}/smp_affinity"
echo 1 > /proc/irq/"${i}"/smp_affinity
done

echo "grep iwlwifi /proc/interrupts"
grep iwlwifi /proc/interrupts

Move the systemd slices away

das@t:~/Downloads$ cat /etc/systemd/system.conf | tail -n 5
#DefaultLimitNICE=
#DefaultLimitRTPRIO=
#DefaultLimitRTTIME=
#DefaultOOMPolicy=stop
CPUAffinity=2-16

das@t:~/Downloads$ cat /etc/systemd/user.conf | tail -n 5
#DefaultLimitMSGQUEUE=
#DefaultLimitNICE=
#DefaultLimitRTPRIO=
#DefaultLimitRTTIME=
CPUAffinity=2-16

I'm unclear why this helps so much, and definitely need to spend more time in analysis