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

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 31 May 2013 18:44:03 +0200
Damien Millescamps <damien.millescamps@6wind.com> wrote:

> On 05/31/2013 05:45 PM, Stephen Hemminger wrote:
> > 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.
> Hi Stephen,
> 
> You didn't really address my point, because the Linux documentation says
> something doesn't mean it works in the real world.
> 
> If you take the example of the hugepages, they have been in the Linux
> kernel since 2.6.28, but the last fix was pushed in 2.6.37 and before
> 2.6.33 it is just impossible to do something with hugepages.
> If you take a look at section 2.3.2 of the DPDK getting started:
> http://www.intel.com/content/dam/www/public/us/en/documents/guides/intel-dpdk-getting-started-guide.pdf,
> you will find that this issue is at least partially addressed.
> 
> So the point is that the topology information being theoretically
> correct on all kernel Linux supported by the DPDK, but the information
> being practically wrong on versions prior to kernel 3.3 means that the
> "fix" is breaking the support for a quite huge range of kernel versions...
> So maybe there might be a better way to get this node information on all
> kernel still currently supported by the DPDK.
> 
> Cheers,

I will just state what we saw. /proc/cpuinfo was wrong on several Dell machines
but sysfs is correct. And since are working on a product, not generic
DPDK, there is no motivation to work on older kernels.

I can dig out the email back and forth with the kernel developers to show that
/proc/cpuinfo is not intended to report anything useful for NUMA related API
if you want.