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X86_FEATURE_CONSTANT_TSC is a Linux-defined, synthesized feature flag. It is used across several vendors. Intel CPUs will set the feature when the architectural CPUID.80000007.EDX[1] bit is set. There are also some Intel CPUs that have the X86_FEATURE_CONSTANT_TSC behavior but don't enumerate it with the architectural bit. Those currently have a model range check. Today, virtually all of the CPUs that have the CPUID bit *also* match the "model >= 0x0e" check. This is confusing. Instead of an open-ended check, pick some models (INTEL_IVYBRIDGE and P4_WILLAMETTE) as the end of goofy CPUs that should enumerate the bit but don't. These models are relatively arbitrary but conservative pick for this. This makes it obvious that later CPUs (like Family 18+) no longer need to synthesize X86_FEATURE_CONSTANT_TSC. Signed-off-by: Sohil Mehta <sohil.mehta@intel.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20250219184133.816753-14-sohil.mehta@intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.