Re: QUESTION: Network hangs with BP6 and 2.4.x kernels, hardware

[Manfred Spraul]

Let's decode it:

> IO APIC #2...... 
> NR Log Phy Mask Trig IRR Pol Stat Dest Deli Vect: 
> 12 0FF 0F 0 1 0 1 0 1 1 91 
> 13 0FF 0F 0 1 1 1 0 1 1 99 

IRR for interrupt 19 is set, that means the IO APIC has sent the
interrupt to a cpu but not yet received the corresponding EOI.

That bit is read only, so we can't set it to 0 to kick the io apic.

The Vector is 99, we must check that bit in the ISR, TMR and IRR of both
cpus.

cpu1:
> ISR: all bits 0
> TMR: only bit 0x99 is set
> IRR: all bits 0

cpu0:
> ISR: all bits 0
> TMR: only bit 0x89 is set
> IRR: bit 0xfc and bit 0xef are set.

ISR is the in-server register, 0 means that the cpu is not processing an
interrupt right now.

TMR is the trigger mode registers, 1 means that the local apic should
send an EOI to the io apic when the cpu signals the EOI to the local
apic.

IRR is the list of pending interrupts:
0xef is the local timer interrupt,
0xfc is the reschedule interrupt
(see include/asm-i386/hw_irq.h)

These bits are also read only.

If you search the IO APIC documentation: number 29056601 - just search
with google. The local APIC is documented in the main cpu handbook (PPro
or later), in the chapter about multiple processor management 

--
	Manfred