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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
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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