linux-kernel - Re: CPU numbering & hyperthreading

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Date:	Tue, 18 Jul 2006 12:03:15 -0700
From:	"Keith Mannthey" <kmannth@...il.com>
To:	"Andrew Athan" <aathan_linux_kernel_1542@...akmail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: CPU numbering & hyperthreading

On 7/17/06, Andrew Athan <aathan_linux_kernel_1542@...akmail.com> wrote:
>
> On an Intel Xeon dual CPU machine running 2.6.16 and up...
>
> I have two highly CPU/memory/network intensive processes with 3-5
> threads each.  I am using sched_setaffinity calls to make sure these two
> processes never compete for the same physical CPU.  Am I right to assume
> that CPU #0 and #1 vs CPU #2 and #3 are separate physical CPUs on a
> 2-CPU w/ hyperthreading box?
>
> I've spent some time looking, but I did not find documentation on
> exactly how CPUs are numbered in a hyperthreaded box.

It is up to the bios how the cpus are layed out.  Any easy way to
check for the info you want is to look at /proc/cpuinfo (you can also
get the info out of /sys/devices/system/cpu/cpu[x]/topology).  Cpus
with the same physical id are in the same package.  The info (core_id
core_siblings  physical_package_id  thread_siblings
and like kind from proc) describes the topology.

Thanks,
  Keith
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