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.
