Description jiayingbao 2025-12-02 14:54:13 UTC

Description of problem:
backport one patch from upstream that use mwait over of halt which can improve the latency. details copy from commit msg:

 The below table represents the exit latency for HLT and MWAIT on AMD
    Zen 3 system. Exit latency is measured by issuing a wakeup (IPI) to
    other CPU and measuring how many clock cycles it took to wakeup.  Each
    iteration measures 10K wakeups by pinning source and destination.

    HLT:

    25.0000th percentile  :      1900 ns
    50.0000th percentile  :      2000 ns
    75.0000th percentile  :      2300 ns
    90.0000th percentile  :      2500 ns
    95.0000th percentile  :      2600 ns
    99.0000th percentile  :      2800 ns
    99.5000th percentile  :      3000 ns
    99.9000th percentile  :      3400 ns
    99.9500th percentile  :      3600 ns
    99.9900th percentile  :      5900 ns
      Min latency         :      1700 ns
      Max latency         :      5900 ns
    Total Samples      9999

    MWAIT:

    25.0000th percentile  :      1400 ns
    50.0000th percentile  :      1500 ns
    75.0000th percentile  :      1700 ns
    90.0000th percentile  :      1800 ns
    95.0000th percentile  :      1900 ns
    99.0000th percentile  :      2300 ns
    99.5000th percentile  :      2500 ns
    99.9000th percentile  :      3200 ns
    99.9500th percentile  :      3500 ns
    99.9900th percentile  :      4600 ns
      Min latency         :      1200 ns
      Max latency         :      4600 ns
    Total Samples      9997

    Improvement (99th percentile): 21.74%

    Below is another result for context_switch2 micro-benchmark, which
    brings out the impact of improved wakeup latency through increased
    context-switches per second.

    with HLT:
    -------------------------------
    50.0000th percentile  :  190184
    75.0000th percentile  :  191032
    90.0000th percentile  :  192314
    95.0000th percentile  :  192520
    99.0000th percentile  :  192844
    MIN  :  190148
    MAX  :  192852

    with MWAIT:
    -------------------------------
    50.0000th percentile  :  277444
    75.0000th percentile  :  278268
    90.0000th percentile  :  278888
    95.0000th percentile  :  279164
    99.0000th percentile  :  280504
    MIN  :  273278
    MAX  :  281410

    Improvement(99th percentile): ~ 45.46%

commit aebef63cf7ff x86: Remove vendor checks from prefer_mwait_c1_over_halt

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