Linux 6.0 Has Temperature Monitoring For Upcoming AMD CPUs, MWAIT For HPC Customers

Written by Michael Larabel in AMD on 1 August 2022 at 09:30 AM EDT. 6 Comments
Among the early pull requests for the now-open Linux 6.0 merge window (nee Linux 5.20) are a few AMD additions worth mentioning.

First up is the x86/cpu pull that now drops the vendor checks from the "prefer_mwait_c1_over_halt" function. This vendor checking was just for Intel CPUs to use MWAIT over HALT due to issues with older AMD processors. However, with newer AMD Zen processors, using MWAIT over HALT is preferred within the C1 power management code for the Linux kernel as using MWAIT over C1 has lower exit latency / more efficient. This change for Linux 6.0 can mean ~21% lower exit latency on Zen 3 from idle though primarily benefits AMD HPC customers who disable global C-states from the BIOS.

More good news for AMD HPC customers with Linux 6.0.

With the vendor checks dropped, AMD CPUs will now happily use MWAIT over HLT in the generic x86 CPU idle code path. For debugging/comparison purposes there is also support for the "idle=nomwait" kernel option if wanting to avoid using MWAIT and return to the old halt instruction use.

Also notable on the AMD Linux side this Monday morning is the x86/misc pull. This adds more AMD PCI IDs and enables support for more Family 17h and Family 19h models within the k10temp driver for CPU temperature monitoring. Linux 6.0's k10temp driver will have CPU temperature monitoring now working for Family 17h Models A0h to AFh and Family 19h models 60h to 7Fh now that the PCI IDs and CCD offsets are being added.

These new IDs for k10temp likely correspond to additional Zen 4 CPUs beyond what already has been added in prior kernels while the new Family 17h IDs are likely for upcoming AMD Mendocino processors. The upcoming AMD Mendocino processors for budget laptops are 6nm TSMC parts with Zen 2 cores and RDNA2 graphics.

There are some other AMD (and Radeon graphics) goodies coming with Linux 6.0, so stay tuned for the other merges over this next two week period.
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