https://bugzilla.suse.com/show_bug.cgi?id=1203767
Bug ID: 1203767
Summary: Backport AMD ACPI processor idle dummy wait fix
Classification: openSUSE
Product: openSUSE Tumbleweed
Version: Current
Hardware: Other
OS: Other
Status: NEW
Severity: Normal
Priority: P5 - None
Component: Kernel
Assignee: kernel-bugs@opensuse.org
Reporter: dmueller@suse.com
QA Contact: qa-bugs@suse.de
Found By: ---
Blocker: ---
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