6850 shows 16 CPUs?

Simon Gao gao at schrodinger.com
Tue Apr 24 14:27:25 CDT 2007


Check if hyper-threading is enabled in BIOS. That's probably why you see
double processors than you expect. You will want to turn
hypter-threading off since it only causes performance and other problems
with no much real benefit.

Simon

Robert Wilson wrote:
> Hi,
>
> This weekend, I built Debian SMP with kernel 2.6.20-7 and noticed I
> was seeing 16 CPUs on our Dell 6850. Initially, it only saw 8 CPUs,
> kernel 2.6.18-x. Then Monday, one of our RedHat admins built a
> development SMP system and it too reports 16 CPUs, kernel 2.6.9-42.
> Yet when I check the specifications, it looks like we should have
> 7130M, dual-core processors, or a maximum of 8 CPUs. Needless to say,
> I'm a little confused:
>
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 15
> model           : 6
> model name      : Intel(R) Xeon(TM) CPU 3.20GHz
> stepping        : 8
> cpu MHz         : 3192.477
> cache size      : 8192 KB
> physical id     : 0
> siblings        : 4
> core id         : 0
> cpu cores       : 2
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 6
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht t
> m pbe nx lm pni monitor ds_cpl est tm2 cid xtpr
> bogomips        : 6389.12
> [root at lab6850 proc]# grep processor cpuinfo
> processor       : 0
> processor       : 1
> processor       : 2
> processor       : 3
> processor       : 4
> processor       : 5
> processor       : 6
> processor       : 7
> processor       : 8
> processor       : 9
> processor       : 10
> processor       : 11
> processor       : 12
> processor       : 13
> processor       : 14
> processor       : 15
>
> Regardless, the machines run like a bat-out-of-Redmond and we're
> seeing some impressive, GigE performance. With four, GigE streams into
> Intel Pro/1000 MT, dual-port cards, it looks like we can get 70% of
> full bandwidth, 64B packets before seeing errors.
>
> What I can't figure out is why the kernel is reporting twice the
> number of CPUs as expected.
>
> One other 'strangeness' is the dual-port, Intel Pro/1000 MT in slot 2
> seems to be quite happy. I installed it with the power cords pulled
> from the box. Yet curiously, the "PowerEdge Additional Information"
> warns against this. Needless to say, this is amusing . . . it
> shouldn't work but there it is. We have all four 'eth' devices
> although under debian and a kernel.org built kernel, they are listed
> as 'eth0, eth1, eth4, eth5', the Intel Pro/1000 MT cards. The
> Broadcom, Teragon drivers are attached to 'eth2 and eth3'. The RedHat
> 2.6.9-42 shows them as 'eth0, eth1, eth2, eth3' with the Broadcoms on
> 'eth4, eth5'.
>
> Thanks,
> Bob Wilson
>
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