For some time now, Intel has been working on the APX extension, which adds more working registers to x86 CPUs along with other improvements that should make the x86 instruction set more competitive with, say, Arm processors. APX will be introduced in Intel Core Ultra 4000 “Nova Lake” CPUs. We assumed that it would take time for software to utilise it, and that it would initially be of little use. That turns out to not be the case.
We covered the APX (Advanced Performance Extensions) extension in a separate article. Some time ago it was confirmed that this technology is to be launched in Nova Lake processors, which will reach the market soonish around the turn of the year, and APX could thus help them achieve higher performance compared to Apple’s processors, but also, for example, AMD’s competing x86 chips. AMD’s processors will get APX only sometime later in an unspecified future, so for a time, Nova Lake chips will have an advantage over Zen 5 and the upcoming Zen 6 when you run an application that uses APX.
The benefit of APX is estimated at somewhere in the range of 5–15% extra performance, depending on the situation, although this may depend heavily on the nature of the code, and there has so far been no way to confront these expectations with reality. The potential promise of these gains should therefore be taken with a grain of salt.
However, because APX is an instruction extension, software will not use it automatically, but only if programmers add support and recompile the program, which is far from automatic in the Windows software space. This platform is renowned for the fact that, thanks to excellent (and very long) backward compatibility, it can run various old software with no problem. It was therefore usually expected that in the first years APX would not be of much use to Nova Lake processors, and that its use would begin to trickle in only relatively far in the future, once processors with support for this technology become more common.
Windows 11 Is Already Prepared to Use APX
Microsoft, however, apparently intends to start using APX early and aggressively, so this extension could be useful to Intel Nova Lake processors from the start. Screenshots of a toggle that is already prepared for these CPUs in Windows 11 have now leaked onto the internet, showing an option added to the Settings app that will be used for enabling APX support. At the moment the toggle is not exposed, but Twitter user XenoPanther showed what it will look like if it is manually made accessible in the currently available Windows 11 build (29695). Microsoft will probably expose this option on computers with an APX-capable processor after Intel releases the Nova Lake processors.
The “Advanced Performance Extensions (APX)” option is described by the sentence “Let Windows use APX for better performance”. It appears that toggling it will require a computer restart for the change to take effect. APX technology needs the cooperation of the operating system (similar to the earlier AVX and AVX-512 extensions), because it adds registers to the processor whose correct saving and restoring must be taken care of by the operating system when switching between processes.
It is not entirely clear whether this toggle will merely enable the use of APX mode in third-party programs (and without activating it, games and programs would then be unable to use APX despite the presence of the extension in the processor). It is described, however, as enabling the use of APX for Windows, which could mean that the system itself will have APX optimizations added to its code, whether coded manually or generated by compiler through building with the APX option.
The reason APX is not always enabled automatically when the system runs on a processor that supports it is not yet clear from this leak. One reason could be that Microsoft has so far had a relatively short time for long-term testing of the operating system’s behavior in APX mode on the only processor (Nova Lake) that now supports it. The company could therefore initially ship the support in a state where it is disabled by default to exercise caution, letting the user to enable it manually. This avoids problems if some applications or Windows components, for various reasons, turn out to not work correctly after APX is activated, or if unexpected performance drops are discovered in some programs. APX should work without problems with old software, which will simply run as before ignoring the extension, but it cannot be ruled out that some unforeseen side effects will occur somewhere.
In any case, thanks to this early support, it will be possible to run some testing of APX’s benefits in programs quickly after the processors are released.
Source: XenoPanther
English translation and edit by Jozef Dudáš
