On Wed, 18 Jun 2008, Rafael J. Wysocki wrote:

quoted text
> Here you go.  Below is the relevant snippet from the yesterday's linux-next
> dmesg with the patches:
> "x86: I/O APIC: timer through 8259A second-chance"
> "x86: add C1E aware idle function"
> reverted and the appended debug patch applied.
> 
> [    0.108006] TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
> [    0.108006] ..MP-BIOS bug: 8254 timer not connected to IO-APIC
> [    0.108006] ...trying to set up timer (IRQ0) through the 8259A ... <2> failed
> [    0.108006] ...trying to set up timer as Virtual Wire IRQ...<2> works.
> 
> The entire dmesg is at: http://www.sisk.pl/kernel/debug/20080616/dmesg-4.log

 Thanks -- this is very important and useful information as it shows the
exact alternative used.

 With such a configuration the "x86: I/O APIC: timer through 8259A
second-chance" patch should not matter, because the only change it
introduces is an attempt to try the same I/O APIC pin again, but with the
IRQ0 line of the master 8259A enabled.  That's not a terribly unusual 
configuration and nothing should get confused in the system.

 Barring the unlikely possibility of the 8259A actually being wired to 
INTIN2 of the I/O APIC I can see two possible explanations:

1. The 8259A interrupt actually escapes to the CPU somehow and is handled
   as an ExtINTA interrupt.  This would make the code in check_timer()  
   decide it has found a working configuration, while actually it has been
   fooled.

2. There is a bug in this patch or an assumption it makes which results 
   in the state of some component not to be restored correctly.  
   Unfortunately I have no resources to test the 64-bit variation of the 
   code, so something may have escaped my attention.

 I'd like to find out which one is the case -- can you please reapply the
patch and send me the corresponding section of the bootstrap log?  If the
system hangs before you can retrieve the log, please just place:

while (1);

or something like that after the out: label in check_timer().

 Thanks.

  Maciej
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