Linux 5.15.35 released with significant performance fix for Intel Alder Lake

For those using the Linux 5.15 LTS kernel such as Ubuntu 22.04 with the use of this default long term support kernel, Linux 5.15.35 was released today and is a notable point release for backporting a Intel P-State driver fix for Intel Alder Lake systems which achieve much better performance by properly deciding between P and E core selection. Here are some benchmarks on Ubuntu 22.04 LTS with Linux 5.15.35 compared to other kernel options.

It started last week when I noted that Intel Alder Lake CPUs with a mix of P/E cores were seeing rough performance out of the box on the impending Ubuntu 22.04 LTS release and better upgrade to a newer version of the Linux kernel (Linux 5.16+). This article contained many benchmarks showing how Ubuntu 22.04 Linux 5.15 LTS kernel was bad for Intel Hybrid CPUs and also pointing out the patch on Linux 5.16+ needed to improve handling of the Intel P-State driver on these latest generation processors.

A small but important fix backported with Linux 5.15.35.

While this patch has been out and in the mainline since November, following last week’s article, Canonical then went ahead and submitted the patch for inclusion in Linux 5.15 stable. He was picked up from the queue and now published today as part of the point release Linux 5.15.35.

In turn, Ubuntu 22.04 should soon see a stable release update incorporating this fix and other 5.15 LTS fixes. In turn, other Linux distributions built on the Linux 5.15 LTS kernel will also benefit from this performance fix from Alder Lake if they haven’t already backported it themselves. For Alder Lake Linux users, I would still recommend running Linux 5.16+ for the best performance/features, especially since Linux 5.15.35+ out of the box still has Alder Lake graphics disabled by default at unless passing the appropriate i915 kernel module options etc.

To confirm the fix in v5.15.35, I ran some benchmarks of this new kernel version against v5.15.34, the default Ubuntu 22.04 kernel, as well as Linux 5.17 for reference. The benchmarks in this article were performed on a Core i7 12600K “Alder Lake” desktop system. Last week’s article featured the Core i9 12900K processor whereas for this article we were just using a completely different system to highlight the equally significant performance impact of this patch. As mentioned earlier, while this patch mentions the fix for “overclocked” systems, the CPU for testing was running at its base speed and the “overclocked” may just be running in the optimized BIOS configuration / optimal memory configuration .

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Steven L. Nielsen