[dpdk-dev] Feature Discussion: CPU topology detection on FreeBSD

Burakov, Anatoly anatoly.burakov at intel.com
Wed Feb 10 17:01:38 CET 2021

On 29-Jan-21 1:45 PM, Bruce Richardson wrote:
> On Fri, Jan 29, 2021 at 12:52:50PM +0000, Burakov, Anatoly wrote:
>> On 29-Jan-21 10:05 AM, Bruce Richardson wrote:
>>> On Thu, Jan 28, 2021 at 04:07:07AM +0000, Oscar Zhao wrote:
>>>> Hello dpdk devs,
>>>> I would like to discuss the feasibility of implementing CPU topology detection on FreeBSD. Currently both eal_cpu_core_id() and eal_cpu_socket_id() in rte_eal library always return 0 on FreeBSD, making NUMA-aware development impossible without resorting to external libraries or system APIs.
>>>> The CPU topology information is available via sysct kern.sched.topology_spec. The only issue is that the return value is an XML formatted object (see https://forums.freebsd.org/threads/number-of-cpus-and-cores.41299/). (https://forums.freebsd.org/threads/number-of-cpus-and-cores.41299/) I'm not sure how feasible it is to parse XML inside DPDK.
>>>> On a side note, obtaining the physical NUMA node id of a core is easy - sysctl dev.cpu.[cpu#].%domain returns the corresponding node id but I have yet found a straightforward way to detect hyperthreads besides the XML thing.
>>>> Oscar
>>> Even adding in the numa node information would be a welcome start.
>> There's little value in it though, because as far as i'm aware we can't
>> allocate memory on specific NUMA nodes in FreeBSD.
> That is because the NUMA support in FreeBSD was not in place when we first
> did the DPDK port. However, I still see no reason not to start adding it
> now, even if it is only for information purposes at this point.

A lot of DPDK apps will fail to work in this case, because most of them 
will allocate with an explicit NUMA node. So, if you have a NUMA node 
assigned to an lcore but can only allocate from NUMA node 0, any 
allocation explicitly targeting NUMA node 1 will not succeed.


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