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Re: SMP does not work as expected - was: Re: [Xen-users] Checking for SM

To: "Dirk H. Schulz" <dirk.schulz@xxxxxxxxxxxxx>
Subject: Re: SMP does not work as expected - was: Re: [Xen-users] Checking for SMP usage in xen stable
From: Derrik Pates <demon@xxxxxxxxxxxxx>
Date: Sat, 12 Nov 2005 23:22:11 -0500
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Dirk H. Schulz wrote:
>>    Name                  Id    Mem(MB)    CPU        State  Time(s) 
>> Console
>>    Domain-0            0    123                0            r---- 
>> 59931.7          
>>    webdynown01    5    511                1            -b---   
>> 193.5    9605
>>    webstatown01    1    255                0            -b---   
>> 202.9    9601

You have a Xeon, which supports hyperthreading, and Xen treats the
hyperthreaded CPU as two virtual CPUs. That's pretty much typical, and
pretty much the way most OSes see a hyperthreaded CPU.

>> So it seems that on dual processor boards smp is somehow simulated if
>> there is just one processor present.
>> Is this a bug, or does it make sense somehow?

It's not a bug. It does make perfect sense.

>> And now my original question comes up again: How can I - reliably -
>> verify that my xen kernel is running smp code?

Run 'xm info' and look at the 'cores' and 'hyperthreads_per_core'
fields? If there are multiple physical CPUs (or in the case of e.g. a
dual-core Opteron, you'll see 2 cores for each CPU), and
'hyperthreads_per_core' will be 2 on Xeon CPUs and HT-capable P4 CPUs
(assuming you haven't turned off hyperthreading in the BIOS, or passed
arguments to Xen itself causing it to ignore the MP tables).

Derrik Pates

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