Running code on an isolated core

[Vaibhav Jain]

On Mon, Aug 22, 2011 at 10:11 PM, Vladimir Murzin <murzin.v at gmail.com>wrote:

>  On Tue, Aug 23, 2011 at 2:15 AM, Vaibhav Jain <vjoss197 at gmail.com> wrote:
> > Hi,
> > Thanks for replying but I want to do this in a SMP machine.
> > Please help!
> >
> > Thanks
> > Vaibhav Jain
> >
> > On Wed, Aug 17, 2011 at 10:53 PM, Vladimir Murzin <murzin.v at gmail.com>
> > wrote:
> >>
> >> On Wed, Aug 17, 2011 at 11:01 PM, Vaibhav Jain <vjoss197 at gmail.com>
> wrote:
> >> > Hi,
> >> >
> >> > I am looking into running a program on one of the cores which is
> >> > isolated
> >> > (logically offline )
> >> > from the rest of the cores. I have come to that the command
> >> > echo 0 > /sys/device/system/cpu/<core num>/online
> >> >
> >> > will make a core logically offline,
> >> > What I need to do now is to run a program on this offline core. Please
> >> > suggest on how to proceed.
> >> >
> >> > Thanks!
> >> > Vaibhav Jain
> >> > _______________________________________________
> >> > Kernelnewbies mailing list
> >> > Kernelnewbies at kernelnewbies.org
> >> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >> >
> >> >
> >> Hi Vaibhav,
> >>
> >> I think it's impossible to run out a process on unplugged CPU. May be
> >> AMP[1] is what you need, but it's a bit different approach.
> >>
> >> [1]http://en.wikipedia.org/wiki/Asymmetric_multiprocessing
> >
> >
>
> Hi Vaibhav,
>
> There is one more approach, but it's not operate on off-lined CPU.
> Have a look at isolcpu kernel boot option.
> Description in Documentation/kernel-parameters.txt says:
>
> This option can be used to specify one or more CPUs to isolate from
> the general SMP balancing and scheduling algorithms. You can move a
> process onto or off an "isolated" CPU via the CPU affinity syscalls or
> cpuset. <cpu number> begins at 0 and the maximum value is "number of
> CPUs in system - 1". This option is the preferred way to isolate CPUs.
> The alternative -- manually setting the CPU mask of all tasks in the
> system -- can cause problems and suboptimal load balancer performance.
>



Hi,

Thanks again! But I am asked to look into running process only when the cpu
has been logically offlined.
Someone suggested that I should make changes to arch/x_86/kernel/smpboot.c
file in one of the play_dead functions. But I don't know
what these function is doing and what changes should I make. Could you
please give me some idea ?


Thanks
Vaibhav Jain
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