Dell XPS 7390 Intel Ice Lake Performance Hit Hard By A Linux Kernel Regression

At the beginning of the month I wrote about the Dell XPS with Core i7 1065G7 Ice Lake running much slower when upgrading to the development release of Ubuntu 20.04 LTS from 19.10. It turns out the performance hit is due to an upstream kernel regression that's thrashing the performance.

Time has finally allowed to poke more at that Ice Lake laptop, the only one I have for testing, so not sure if it's specific to this Dell XPS laptop or Ice Lake at large. In any case, when running Ubuntu 19.10 and upgrading the kernel, the performance hits are very real... Even beyond Linux 5.4 like used by Ubuntu 20.04 LTS, the wrecked performance is still there on Linux 5.6 stable and Linux 5.7 Git... Testing using the Mainline Kernel PPA.

The mainline kernel builds tested are still on P-State powersave and other fundamental options in common with Linux 5.3 from Ubuntu 19.10. But when moving to the newer kernels, the performance slides very fast:





Graphics hits? Oh yes.












And the hits for other workloads quite brutal too...

The regressions are not due to a change in CPU security mitigations and the CPU frequency scaling governor/driver remained the same.



Even the web browsing performance is dramatically impacted.

So the lower Ubuntu 20.04 performance we saw on this laptop wasn't specific to Ubuntu but does happen on the mainline kernel builds too, including the latest Linux 5.6 stable and Linux 5.7 Git kernels. But in having this lone Ice Lake laptop, at the moment I do not know if it's specific to the Dell XPS 7390 Ice Lake or to all (or some subset of) CPUs of that generation, at least with older Intel laptops I haven't seen such dramatic hits on the older kernels. Kernel bisecting would be quite slow on that Ice Lake CPU, but will poke more at it as time allows (and sanity for bisecting on a 1065G7...) and at least for now is clear why the Ubuntu 20.04 results from earlier this month were so poor on this device and a pity that on Linux 5.6~5.7 upstream it remains wrecked.

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