[Bug 192316] New: Invariant TSC gets misdetected on Intel Core 2 Duo processors, resulting in sluggish system behavior

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192316

            Bug ID: 192316
           Summary: Invariant TSC gets misdetected on Intel Core 2 Duo
                    processors, resulting in sluggish system behavior
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: Any
                OS: Any
            Status: Needs Triage
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: jan.kokemueller at gmail.com

Hi,

On this Intel Core 2 Duo T6570 processor, the TSC timer gets a very high
priority, even though it is not invariant. If there is power saving enabled and
the processor goes to lower C-states, this results in a sluggish system.

Thread on freebsd-current:
https://lists.freebsd.org/pipermail/freebsd-current/2014-July/051498.html

There are some Intel models hard coded as TSC invariant in the TSC detection
logic, even if they are not. Suggested fix: just check if the TSC_INVARIANT
processor bit is set or not. I've attached a patch.

Cheers,
Jan

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