path: root/security/safesetid
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authorDave Hansen <>2022-09-22 11:47:45 -0700
committerDave Hansen <>2022-09-23 15:24:10 -0700
commite400ad8b7e6a1b9102123c6240289a811501f7d9 (patch)
treea6877ba72f28a84fa95b285e49d285ff5d308348 /security/safesetid
parent81fa6fd13b5c43601fba8486f2385dbd7c1935e2 (diff)
ACPI: processor idle: Practically limit "Dummy wait" workaround to old Intel systems
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 <> Suggested-by: Rafael J. Wysocki <> Signed-off-by: Dave Hansen <> Reviewed-by: Mario Limonciello <> Tested-by: K Prateek Nayak <> Link: Link:
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