From mboxrd@z Thu Jan  1 00:00:00 1970
From: Klaas Zweck <khz@tzi.org>
Subject: timer on just one cpu in linux mp-system
Date: Thu, 18 Apr 2002 00:25:07 +0200
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To: linux-smp <linux-smp@vger.kernel.org>

hi,

my question is how to make a linux mp-kernel
react on timer interrupts on just _one_ cpu?

my system is a pentium3 smp computer with
a serverworks chipset.

boot.msg says:

 >Intel MultiProcessor Specification v1.4
<4>    Virtual Wire compatibility mode.
<4>OEM ID: OEM00000 Product ID: PROD00000000 APIC at: 0xFEE00000
<4>Processor #3 Pentium(tm) Pro APIC version 17
<4>    Floating point unit present.
<4>    Machine Exception supported.
<4>    64 bit compare & exchange supported.
<4>    Internal APIC present.
<4>    SEP present.
<4>    MTRR  present.
<4>    PGE  present.
<4>    MCA  present.
<4>    CMOV  present.
<4>    PAT  present.
<4>    PSE  present.
<4>    PSN  present.
<4>    MMX  present.
<4>    FXSR  present.
<4>    XMM  present.
<4>    Bootup CPU

and so for the second cpu (except for the bootup cpu line)
cat /proc/interrupts says that timer interrupt
is number 0 and it is always counted on both cpus.
(they diifer slightly but both counters are updated )

example of cat /proc/interrupts

           CPU0       CPU1
  0:     105123      96263    IO-APIC-edge  timer  

in the function setup_local_APIC() in arch/i386/kernel/apic.c
i did the following to (try) to disable timer interrupt on cpu1:

if ( smp_processor_id() ){
 
          lvtt1_value = SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV) |
              APIC_LVT_TIMER_PERIODIC | LOCAL_TIMER_VECTOR;

--->   lvtt1_value = lvtt1_value | APIC_LVT_MASKED;
          printk( "KHZ: Write to AP local APIC (Timer) %x \n", 
lvtt1_value );
 
        } else {
            lvtt1_value = SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV) |
                APIC_LVT_TIMER_PERIODIC | LOCAL_TIMER_VECTOR;
            printk( "KHZ: Write to BP local APIC (Timer) %x \n", 
lvtt1_value );
} 

---> means my try to mask the timer interrupt for any but the boot cpu.
( since the boot cpu has smp_processor_id() zero ).

but it didn't work since cat /proc/interrupts still reports timer 
interrupts on
both cpus.

even calling clear_local_APIC() at the end of setup_local_APIC()
(both in arch/i386/kernel/apic.c)
which should set all local apic local vector table (LVT) entries to
masked state didn't work.

still cat /proc/interrupts reports timer irqs on both cpus.

what am i doing wrong ??

thanks and greetings,
klaas