Ubuntu 24.04 LTS Leaning Toward Low-Latency Kernel Optimizations By Default

Last month it was noted on Phoronix that Canonical's kernel team is looking at folding their low-latency kernel optimizations into their generic kernel builds. Right now Ubuntu maintains a separate "lowlatency" kernel flavor with Kconfig tweaks in the name of low-latency responsiveness as an alternative to their "generic" kernel default, but for Ubuntu 24.04 LTS it continues looking like they'll move forward with this change of incorporating the changes into their default kernel build.

The Ubuntu low-latency kernel option is basically a few tweaked Kconfig options to better tune the kernel for responsiveness. But to avoid the ongoing QA/build time costs and other maintenance in having this separate "lowlatency" flavor, they have been considering to incorporate the few changes into their generic kernel image. The main concern in doing so was possible throughput performance implications of the changes.

Following that I ran some fresh Ubuntu generic vs. low-latency kernel benchmarks and in the real-world tests there was nothing scary out of the results. Andrea Righi on Canonical's kernel team has also been carrying out some tests. Andrea Righi hasn't found any particularly concerning results and even found the CPU power consumption under load to be slightly lowered with the 1000 Hz configuration than at the 250 Hz generic default.

Andrea Righi posted today a status update on the consideration of having Ubuntu 24.04 LTS pull in the low-latency kernel changes to their generic build. Righi conlcuded:

"Test results do not show any significant performance regression between HZ=1000 vs HZ=250.

Enabling the extra config options also doesn’t seem to introduce significant performance regression and it would provide users the flexibility to adjust the system at boot-time / run-time prioritizing 1) throughput, 2) responsiveness, or 3) power consumption, making the generic Ubuntu kernel even more “generic”.

There might be some special corner cases where these changes can cause performance regressions, but for the majority of the cases they can provide real performance benefits and a much greater flexibility.

Therefore, it seems reasonable to consider including these changes in the next Ubuntu kernel for the 24.04 release."

So it's looking like good chances that Ubuntu 24.04's "generic" kernel default will pull in these low-latency changes barring any major surprises from coming up in the weeks ahead.

Ubuntu 24.04 LTS will be out in April and is planning to be powered by Linux 6.8.