Linux x86 FPU Code Getting Reworked In Preparation For Intel AMX

Written by Michael Larabel in Intel on 12 October 2021 at 05:45 AM EDT. 17 Comments
It's been one year now that Intel has been posting Linux kernel patches to enable AMX support for upcoming Sapphire Rapids processors. Over the past year their Linux kernel patches for enabling Advanced Matrix Extensions has gone through 11 rounds of review but that journey isn't over yet.

Thomas Gleixner sent out a set of patches today cleaning up Linux's existing x86/FPU code and making other alterations ahead of AMX support landing. The clean-up is being pursued now since "the recent attempts to support the new AMX feature just tried to bolt it into the existing FPU code...As demonstrated with the supervisor bits, that's not really sensible and leads to similar issues." Thus the x86 FPU code is being cleaned up now and AMX patches being reworked for better integration.

These 31 patches cleaning up the existing FPU code are just part one of a planned four part series. Further changes to the FPU code are being worked out with the other series currently available from a Git branch.

The actual AMX patches have been "significantly reworked" to adjust to these prep changes and correct prior shortcomings in the code.

So the AMX enablement code is moving ahead but is now more involved and not immediately clear when the code will be ready for merging like if it will be ready for the upcoming 5.16 merge window. Intel has communicated they plan to ramp up Sapphire Rapids production in Q2 and hopefully by then -- as well as for distributions like Ubuntu 22.04 LTS -- the AMX support will have been upstreamed in time and found in distribution kernels and toolchains but it's getting rather close.
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