Difference between logical and physical cpu hotplug

[Vaibhav Jain]

Thanks for the reply!
I am looking for a little more detail.

Thanks


On Tue, Aug 16, 2011 at 10:26 PM, Vladimir Murzin <murzin.v at gmail.com>wrote:

> On Wed, Aug 17, 2011 at 9:14 AM, Vaibhav Jain <vjoss197 at gmail.com> wrote:
> > Hi,
> >
> > I need to know the difference between making a cpu logically offline
> > and physically offline. I have read that the following command
> >
> > $ echo 0  > /sys/device/system/cpu/<cpu number>/online
> >
> > makes a cpu logically offline. It frees the cpu from interrupts and
> migrates
> > running processes.
> > But then what does it mean to make a cpu physically offline ?
> > I referred to following article :
> >
> > http://www.kernel.org/doc/Documentation/cpu-hotplug.txt
> >
> > Here is the relevant excerpt :
> >
> > Q: Does hot-add/hot-remove refer to physical add/remove of cpus?
> > A: The usage of hot-add/remove may not be very consistently used in the
> > code.
> > CONFIG_HOTPLUG_CPU enables logical online/offline capability in the
> kernel.
> > To support physical addition/removal, one would need some BIOS hooks and
> > the platform should have something like an attention button in PCI
> hotplug.
> > CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of
> > CPUs.
> >
> > Please help!
> >
> > Thanks
> > Vaibhav Jain
> >
> > _______________________________________________
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> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >
> >
> Hi Vaibhav!
>
> I think physical CPU hot-plug is a capability to plug in and out
> processing device (CPU) on running machine. Logical CPU hot-plug is a
> capability to add on and remove out already available processing units
> (CPU s or cores) under SMP domain of OS.
>
> P.S. Sorry for my weak English.
>
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