only one logical CPU used in Xeon

Won De Erick won.derick at
Tue Mar 10 07:55:49 PDT 2009


I also have boxes with several Intel Xeon dual-core processors, and also got same results. 

With FreeBSD 6.2R:
#sysctl -a | grep pci.enable
hw.pci.enable_io_modes: 1    

I think 6.2 uses legacy interrupt (INTx) which allows sharing of IRQs and is CPU bounded(?). It is also probable that even MSI/MSIX-supported NIC drivers are used here, 6.2R still used the traditional interrupt mechanism.

With FreeBSD 7.1:
#sysctl -a | grep pci.enable
hw.pci.enable_msix: 1
hw.pci.enable_msi: 1
hw.pci.enable_io_modes: 1

Google would tell us that MSI/MSI-X allows control over which processor is chosen as the interrupt target. Does this explain the result?



--- On Tue, 3/10/09, Robert Heron <robert at> wrote:
> Hi,
> I have FreeBSD 6.2R running on Intel SE7501HG2 motherboard
> with two Xeon installed.
> System detects 2 CPUs with 2 cores in each of them (total 4
> cores) but it uses only one core in each Xeon (total 2 of 4
> cores are used only).
> I see it in the 'top'. I tried the same hardware on FreeBSD
> 7.1R and this OS uses all of the detected cores.
> What should I do FreeBSD 6.2R to use all of the available
> cores?
> I cannot upgrade it to 7.x, must use 6.x
> Regards,
> Robert Heron


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