02e61196c5
commit e400ad8b7e6a1b9102123c6240289a811501f7d9 upstream. Old, circa 2002 chipsets have a bug: they don't go idle when they are supposed to. So, a workaround was added to slow the CPU down and ensure that the CPU waits a bit for the chipset to actually go idle. This workaround is ancient and has been in place in some form since the original kernel ACPI implementation. But, this workaround is very painful on modern systems. The "inl()" can take thousands of cycles (see Link: for some more detailed numbers and some fun kernel archaeology). First and foremost, modern systems should not be using this code. Typical Intel systems have not used it in over a decade because it is horribly inferior to MWAIT-based idle. Despite this, people do seem to be tripping over this workaround on AMD system today. Limit the "dummy wait" workaround to Intel systems. Keep Modern AMD systems from tripping over the workaround. Remotely modern Intel systems use intel_idle instead of this code and will, in practice, remain unaffected by the dummy wait. Reported-by: K Prateek Nayak <kprateek.nayak@amd.com> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com> Link: https://lore.kernel.org/all/20220921063638.2489-1-kprateek.nayak@amd.com/ Link: https://lkml.kernel.org/r/20220922184745.3252932-1-dave.hansen@intel.com Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 Restructured Text 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.