Message-ID: <42637607.7050207@in.ibm.com>
Date: Mon, 18 Apr 2005 14:25:35 +0530
From: Sripathi Kodi <sripathik@in.ibm.com>
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To: linux-kernel@vger.kernel.org
CC: discuss@x86-64.org
Subject: x86_64: How to disable local APIC timer interrupts?
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Hi,

I am trying to disable the local APIC timer interrupts on x86_64
machine, but finding that it just doesn't work. I am trying to find out
if I am doing something wrong or if there is a problem with these CPUs.

I have a dual-cpu x86_64 machine and I have booted up with 2.6.11 kernel
and nmi_watchdog=2. I called disable_APIC_timer() function, which seems
to be setting the 16th bit of the APIC timer register, which is what the
AMD document suggests to disable the timer. This function is in fact
__init, but I changed it not to be so. I noticed that we continue to see
local APIC timer interrupts on the very CPU where I called
disable_APIC_timer. I have a printk in smp_apic_timer_interrupt() to
verify this. Booting the machine with maxcpus=1 didn't have any effect
on the outcome. CPUs are of the following type:

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 5
model name      : AMD Opteron(tm) Processor 248
stepping        : 8
cpu MHz         : 2193.510
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext lm 
3dnowext 3dnow
bogomips        : 4325.37
TLB size        : 1088 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts ttp

Please let me know if I am doing something wrong and if I should do
something else to disable local APIC timer interrupts. I need to disable
these interrupts to solve a problem in LKCD dumping.
smp_apic_timer_interrupt eventually calls update_process_times, which is
causing problem in a particular LKCD dump case I am looking at.

Please copy me on your reply, as I have not subscribed to the list.

Thanks and regards,
Sripathi.
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