Non-identical CPUs in dual-processor system

Tony Shadwick tshadwick at goinet.com
Fri May 20 05:38:23 PDT 2005


My general thoughts on the matter is that if the bios is happy and letting 
you boot up multi-cpu, then you should be fine.  The OS is going to throw 
instructions at the two cpu's, and those instructions will be run.

The only real difference between any chips that are i386-compatible that 
you insert in there are transistor sizes, and probably some 
brand-specific-deal that identifies brand name, model number, and 
chip-specific instructions (such as MMX).

At the end of the day, you're sending x86 instructions to an x86 
compatible cpu.  I would think you're fine.  If the OS is correctly 
measuring the load on the cpus, I twould think it should balance that load 
nicely, just be sure to compile your apps for threading where it's 
supported (perl comes to mind).

Tony

On Thu, 19 May 2005, Brian O'Shea wrote:

> Hello all,
>
> I have a dual-processor system that I have been using with only a
> single CPU for some time.  Recently I got ahold of another CPU from
> an old retired system.  I thought that both processors were identical
> (they came from what appears to be the same model PC, an HP Kayak XU).
> However, after booting the system I see that the processors are not
> the same:
>
> CPU information in mptable output:
>
> Processors:     APIC ID Version State           Family  Model   Step    Flags
>                 0       0x11    BSP, usable     6       3       3
> 0x80fbff
>                 1       0x11    AP, usable      6       5       2
> 0x183fbff
>
> (sorry for the long lines)
>
> In this output you can see that the model for CPU0 is 3, but for
> CPU 1 it is 5.  Also, the flags are different.  Are there likely to
> be any adverse effects from using this combination of processors?
> There are no errors in dmesg, and the system appears to be using
> both processors:
>
> ...
> CPU: Pentium II/Pentium II Xeon/Celeron (266.08-MHz 686-class CPU)
>  Origin = "GenuineIntel"  Id = 0x633  Stepping = 3
>
> Features=0x80fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,MMX>
>
> ...
> MPTable: <HP       XU/XW       >
> FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
> cpu0 (BSP): APIC ID:  0
> cpu1 (AP): APIC ID:  1
>
> ...
> cpu0 on motherboard
> cpu1 on motherboard
>
> ...
> SMP: AP CPU #1 Launched!
>
> Thanks,
> -brian
>
>
>
>
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