linux-kernel - dell r610, 16-cores, interrupt issue

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Date:	Thu, 19 Nov 2009 14:16:50 +0100
From:	Jasper Spaans <spaans@...-it.com>
To:	<linux-kernel@...r.kernel.org>
Subject: dell r610, 16-cores, interrupt issue

Hi lists,

I'm working on setting up a Dell R610 machine with two quadcore Xeons an
hyperthreading, giving a total of 16 CPUs.

When using the current head, with CONFIG_NR_CPUS=16, this gives me
unexpected irq handling:

spaans@...0 ~ $ cat /proc/interrupts 
            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7       CPU8       CPU9       CPU10      CPU11      CPU12      CPU13      CPU14      CPU15      
   0:     230366          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-edge      timer
   1:          2          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-edge      i8042
   8:        114          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-edge      rtc0
   9:          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-fasteoi   acpi
  12:          4          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-edge      i8042
  16:       2220          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC-fasteoi   ioc0
...
  61:    1456518          0          0          0          0          0          0          0          0          0          0          0          0          0          0          0   PCI-MSI-edge      eth4
...

so, all external interrupts seem to end up being handled by CPU0.

When doing the same with CONFIG_NR_CPUS=8, each interrupt source is given
its own CPU to be used to handle those interrupts, but there's only one CPU
for each IRQ.

Furthermore, nothing seems to be weird in /proc/irq/*/smp_affinity, that is:
all bits are set there.  If I disable the first CPU for an irq, the next CPU
will start receiving interrupts:

r610 61 # echo fffe >smp_affinity 
r610 61 # cat /proc/interrupts 
...
  61:    4392347      35086          0          0          0          0          0          0          0          0          0          0          0          0          0          0   PCI-MSI-edge      eth4
...


Is this supposed to happen, is it a bug, or did I make a configuration
booboo somewhere?

The configuration (grep -v '^#'-d) is attached, as is the dmesg.

Thanks,
Jasper
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View attachment "r610-conf-head.txt" of type "text/plain" (34066 bytes)

View attachment "dmesg1.txt" of type "text/plain" (85912 bytes)