Linux 5.15.35 Released With Important Performance Fix For Intel Alder Lake
For those making use of the Linux 5.15 LTS kernel such as Ubuntu 22.04 with using this long-term support kernel by default, Linux 5.15.35 is out today and is a notable point release for back-porting an Intel P-State driver fix for Intel Alder Lake systems that leads to much better performance in properly deciding between P and E core selection. Here are some benchmarks on Ubuntu 22.04 LTS with Linux 5.15.35 against other kernel options.
It started out last week where I noted Intel Alder Lake CPUs with a mix of the P/E cores was seeing rough performance out-of-the-box on the imminent Ubuntu 22.04 LTS release and would be better off moving to a newer version of the Linux kernel (Linux 5.16+). That article had many benchmarks showing how Ubuntu 22.04's Linux 5.15 LTS kernel was in rough shape for Intel hybrid CPUs and also pointing out the patch in Linux 5.16+ that is needed for improving the Intel P-State driver handling on these latest-generation CPUs.
While that patch has been out and in mainline since November, following last week's article, Canonical then went ahead and submitted the patch for inclusion in Linux 5.15 stable. It was picked up into the queue and now released today as part of the Linux 5.15.35 point release.
In turn Ubuntu 22.04 should see a stable release update soon pulling in this and other 5.15 LTS patches. In turn other Linux distributions relying on the Linux 5.15 LTS kernel will also enjoy this Alder Lake performance fix if they haven't already back-ported it themselves. For Alder Lake Linux users though I'd still recommend running Linux 5.16+ for the best performance/features, especially as Linux 5.15.35+ out-of-the-box still have Alder Lake graphics disabled by default unless passing the appropriate i915 kernel module option, etc.
For confirming the fix in v5.15.35, I ran some benchmarks of this new kernel release compared to v5.15.34, Ubuntu 22.04's default kernel, and also Linux 5.17 for reference. The benchmarks in this article were carried out on a Core i7 12600K "Alder Lake" desktop system. Last week's article was featuring the Core i9 12900K processor while for this article just using a completely different system for highlighting the equally significant performance impact of this fix. As mentioned before, while this patch mentions the fix for "overclocked" systems, the CPU for testing was running at its stock speeds and the "overclocked" can simply be running in the optimized BIOS configuration / optimal memory configuration.