erlang:system_info(cpu_topology) strange behavior

[Frank Muller]

Thanks Rickard.

8 oct. 2020 at 19:47, Rickard Green <rickard@REDACTED> wrote

> On Thu, Oct 8, 2020 at 7:36 PM Frank Muller <frank.muller.erl@REDACTED>
> wrote:
>
>> Answering my own question.
>>
>> The second attempt worked because I was under “root”.
>>
>> Attaching to the release with -remsh failed because the node was running
>> under user “orca” which has less privileges.
>>
>> Is this an expected behavior?
>>
>> /Frank
>>
>>
> The runtime system gets the information about cpu topology by reading
> files under /sys/devices/system/. If it cannot read and parse the files
> there, it will fail to detect the cpu topology. Seems like only root is
> allowed to read that part of the file-system in your case.
>
> Regards,
> Rickard Green
>
>
>
>> Frank<frank.muller.erl@REDACTED>
>>
>>> Hi guys,
>>>
>>> When I attached (-remsh) to my release application (/opt/orca), this
>>> call returns undefined:
>>>
>>> (orca@REDACTED)1> erlang:system_info(cpu_topology).
>>> undefined
>>>
>>> If try this instead, the call seems to work as expected:
>>>
>>> $ /opt/orca/erts-10.7.2.4/bin/erl
>>> 1> erlang:system_info(cpu_topology).
>>> [{processor,[{core,[{thread,{logical,0}},
>>>                     {thread,{logical,4}}]},
>>>              {core,[{thread,{logical,1}},{thread,{logical,5}}]},
>>>              {core,[{thread,{logical,2}},{thread,{logical,6}}]},
>>>              {core,[{thread,{logical,3}},{thread,{logical,7}}]}]}]
>>>
>>>
>>> I’m on Ubuntu16 LTS kernel 4.4.0, Erlang 22.3.4.11.
>>>
>>> Help appreciated
>>>
>>> /Frank
>>>
>>
>
> --
> Rickard Green, Erlang/OTP, Ericsson AB
>
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