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    SubjectAPIC errors ...

    lately having upgraded my DUal-BX motherboard to two PIII-850 CPUs, I run
    into some trouble.
    FIrst, I had had an assymetric configuration (iPIII-850 + iPII-350) , which
    Linux did not support; I created a fix and sent it to LKML. It worked
    perfectly, i.e. without the problems described below.

    Now, I have two iPIII-850, but I run into different kind of troubles:
    (a) The BIOS will sometimes not recognize the second CPU
    (b) Linux reports APIC errors and occasionally stops to process IRQs on the
    second CPU or crashes (2.4.x kernel).

    Some details: DFI P2XBL/D, i440BX, BIOS Award mid 2000 (MPS 1.4), microcode
    patches end 2000 patched into BIOS (which yields the rev. 08 for my pIII
    (868)). The board is unable to supply the needed 1.7V for the CPUs,
    therefore the Slot Adapter (from PowerLeap) contains voltage regulators and
    VID is faked to 2.2V. The mainboard by specs supports up to 800MHz (max
    multiplier 8 with FSB 100MHz).

    The config should be fine; the nmultipliers are fixe anyway nowadays. However:
    (a) If I explicitly specify 100, 103 or 112 MHz FSB freq., the second CPU is
    not recognized by the BIOS (and subsequently not by Linux) most of the
    times. If set to automatic (yields 100MHz), it always recognizes the
    2nd CPU. Strange! Setting 83, 75, or 66 MHz FSB, the 2nd CPU is
    recognized as well.
    (b) The 2.2.16 kernel seems to be happy (did not run long enough to really
    check stability), but the 2.4.x kernels reports lots of APIC errors.
    Lots is smth in between 1/minute (almost idle computer) and more than
    1/second (gears Meas demo running). After some time, eventually the 2nd
    CPU does not get IRQs any more; I've even seen some lockups (after a
    day or so) of Linux, which I'm not used to :-(
    Going back to 83/75/66 MHz FSB seems to also solve this problem, but
    is not considered a solution by me.

    Here's some excerpt: (dmesg)
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 01(01)
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 01(05)
    APIC error on CPU1: 02(02)
    unexpected IRQ trap at vector d0
    unexpected IRQ trap at vector 88
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 05(01)
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 01(01)
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 01(01)
    APIC error on CPU0: 01(01)
    APIC error on CPU1: 02(02)
    APIC error on CPU0: 01(01)

    pckurt:~ # cat /proc/interrupts
    CPU0 CPU1
    0: 5180522 2357505 IO-APIC-edge timer
    1: 24284 15803 IO-APIC-edge keyboard
    2: 0 0 XT-PIC cascade
    3: 2 0 IO-APIC-edge
    4: 0 2 IO-APIC-edge serial
    5: 35031 27240 IO-APIC-edge snd-card-als100 - DSP
    6: 1 2 IO-APIC-edge
    7: 2 0 IO-APIC-edge parport0
    8: 0 1 IO-APIC-edge rtc
    10: 1 0 IO-APIC-edge snd-card-als100 - MPU-401
    12: 5124 5959 IO-APIC-edge PS/2 Mouse
    14: 18953 18258 IO-APIC-edge ide0
    17: 21728 20208 IO-APIC-level eth0
    18: 23418 22327 IO-APIC-level sym53c8xx
    19: 9553 9442 IO-APIC-level aic7xxx, bttv
    28: 0 13 none
    136: 0 35 none
    140: 0 3 none
    152: 0 1 none
    156: 0 2 none
    160: 0 2 none
    172: 0 14 none
    200: 0 1 none
    204: 0 2 none
    208: 0 13 none
    NMI: 0 0
    LOC: 7538766 7538742
    ERR: 777

    (Note that I patched the IRQ reporting stuff, so you can get a count for
    bogus IRQ vectors.) The AGP slot (MGA400) is mapped to IRQ16. (Not visible

    As you can see, the APIC on CPU1 seems eems to suffer under noise!
    It gets APIC errors (which it acknowledges and causes CPU0 to also get an
    error) and occasionally receives bogus IRQ vectors.

    So this looks like a HW problem. Some reports on LKML seem to indicate that
    this is indeed the case.

    Somebody is talking about the voltage regulators not giving a really stable
    voltage (without load?) causing the noise. A resistor with a capacitor
    should help then ... However, sensors reports 2.20V without any flakiness.
    Any details on this known?
    It could also be that the MoBo chipset (IO-APIC?) has problems to recognize
    the signals from 1.7V CPUs expecting at least 1.8 (or 2.2) V. Maybe faking
    the VID to 2.0V instead of 2.2V would be useful then.

    I would be thankful for any knowledge on this issue!

    (As this is slightly off-topic, you may reply via PM. If I happen to solve
    my problems, I'll post a summary to LKML.)

    Kurt Garloff <> [Eindhoven, NL]
    Physics: Plasma simulations <K.Garloff@Phys.TUE.NL> [TU Eindhoven, NL]
    Linux: SCSI, Security <> [SuSE Nuernberg, FRG]
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