[dpdk-dev] [PATCH 0/7] Vyatta patches

[Stephen Hemminger]

On Fri, 31 May 2013 11:29:09 +0200
Damien Millescamps <damien.millescamps at 6wind.com> wrote:

> On 05/30/2013 07:12 PM, Stephen Hemminger wrote:
> > One fix not included is the NUMA cpu assignment. The original Intel code
> > in 1.2 incorrectly used /proc/cpuinfo to try and assign CPU's to NUMA socket.
> > The problem is that /proc/cpuinfo physical_id corresponds to what the BIOS
> > tells the kernel and is intended for messages only. For example, on our
> > Dell boxes the first CPU and only CPU is reported as physical_id 1!
> > The fix is to use sysfs instead,
> Hi Stephen,
> 
> Are you using the
> /sys/devices/system/node/nodeX/cpuX/topology/physical_package_id special
> file ?
> 
> If so, then it is only usable starting from Kernel 3.3 according to this
> fix:
> http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=64be4c1c2428e148de6081af235e2418e6a66dda
> 
> The value returned for kernel prior to 3.3 is really not better than the
> one from /proc/cpuinfo, so that's kind of a robbing Peter to pay Paul
> example...
> 
> There is obviously a problem with the NUMA node ID detection right now
> since both /proc/cpuinfo and /sys can return incorrect values, however
> the node and cpu numbering is always good in the kernel boot log from
> what I know. So there might be a better way to find the real node ID
> whatever the kernel version used.
> 
> Cheers,

You need to use /sys/devices/system/cpu/cpuN/topology/physical_package_id
as documented in kernel (Documentation/cputopology.txt).
This was confirmed by several kernel developers including Andi Kleen from
Intel. The value in /proc/cpuinfo comes from the APCI tables and is the value
reported by the BIOS. There are machines that report socket 1 and 2.
Haven't played with older kernels, but the topology information in sysfs
has existed since 2.6.16.

The final Intel solution was to use physical_packate_id and fall back
to /proc/cpuinfo as last resort.