Ubuntu variant optimized with x86-64-v3

Midway through last year, an announcement was made  on the Ubuntu forum: starting with the 25.10 release, they would provide additional variants for some packages. These packages are built with amd64v3 optimizations. While not every package is included, they initially planned to target around 2,000 of them. Discussions around this started even earlier, two years ago  .

Let me quickly summarize to provide some context. The idea is quite simple: most widely used Linux distributions use conservative CPU optimization flags to maintain backward compatibility. They need to run safely on a variety of hardware, including older systems. Currently, they rely on basic x64 optimizations that target CPUs from 2003-2004 (such as Intel Prescott or AMD K8) - and let’s be honest, not many people still use those. While CPU development may have slowed compared to the past, many new technologies have been delivered over the last 20 years. Specific instructions can improve multimedia processing, optimize power usage, and more.

The question is: where do we draw the line? What should be the “bare minimum” supported CPU?

That is not easy to answer. There are many different CPUs which, even within the same generation, can support different instruction sets. To address this, a series of optimization “levels” was proposed. For an in-depth description, check the linked article¹. Most CPUs produced after 2015 already support x86-64-v3, which covers SSE, AVX, and several other instruction sets. The v4 level also requires AVX512 support, which AMD Ryzen CPUs handle well, but many Intel chips do not. That said, x86-64-v3 feels like a proper, even conservative, optimization set for 2026. However, not many distributions are currently implementing it. Funny enough, Linus Torvalds criticized it a lot too².

Ubuntu wanted to change this without causing too much breakage. They decided to provide alternative architecture binaries. Just as we have x86 and arm architectures, we can now have another variant of x86. Initially, this was built once for testing (around 2 years ago) to check the impact, and the results were positive. To my delight, for version 25.10, they provided this alternative repository that we can all configure and test. As I understand it, they plan to continue this approach and extend it for the upcoming Ubuntu 26.04 LTS, allowing users to choose between default or optimized binaries.

With the new Ubuntu 26.04 coming soon, I was curious to see how it works, so I decided to use x86-64-v3 on my local desktop, still running 25.10. As a former heavy Gentoo user (20 years ago), I was expecting some instability, but nothing like that happened. Let me share how to set it up, as the method described on the forum is not optimal - it enables the custom architecture for all repositories, which causes issues with non-standard sources (like PPA’s).

Try it out

To be on the safe side, check if your system can switch:

ld.so --help | grep '\-v[0-9]'
  x86-64-v4
  x86-64-v3 (supported, searched)
  x86-64-v2 (supported, searched)

I am using an Intel i5-14600K. It lacks AVX512, so I cannot use v4, but v3 works perfectly.

Now, update your /etc/apt/sources.list.d/ubuntu.sources. The script below will update the Architectures field if it is already present or add it if it is missing:

FILE=/etc/apt/sources.list.d/ubuntu.sources
VALUE="Architectures: amd64v3"

if grep -q '^Architectures:' "$FILE"; then
  sudo sed -i "s/^Architectures:.*/$VALUE/" "$FILE"
else
  echo "$VALUE" | sudo tee -a "$FILE" > /dev/null
fi

Next, update your sources and upgrade dpkg first (this step is important):

apt update
apt install dpkg

Now you can upgrade the rest of the system:

apt upgrade -y

You may see a warning about “downgrading” packages, but this is simply due to tool readiness. The team has promised to resolve this in the final Ubuntu 26.04 release.

How does it perform?

I switched more than a month ago. While I haven’t performed formal benchmarks, I was more concerned about stability and potential edge-case issues.

From my time using Gentoo, I remember that aggressive optimizations could sometimes worsen performance or cause instability due to less-tested CPU paths. I am particularly interested in using these optimizations on servers, where the benefits - such as faster cryptography and arithmetic - could significantly outweigh the advantages for desktop use.

Happily, over the past two months, I haven’t experienced any issues.

I am looking forward to Ubuntu 26.04, where these optimizations should be available with even wider package coverage.

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