Re: CPU numbering & hyperthreading

From: Keith Mannthey
Date: Tue Jul 18 2006 - 15:01:52 EST

On 7/17/06, Andrew Athan <aathan_linux_kernel_1542@xxxxxxxxxxxxx> 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.

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