Wrong CPU count on Apollo Lake platform

Wrong CPU count on Apollo Lake platform

[dabbede]

Dear Xenomai community,

I'm writing here because of the following issue: I have compiled a
xenomai-patched kernel that, when used on an Intel Atom E3950 (Apollo
Lake family), return the wrong cpu count (i.e. nproc returns 1 instead
of 4, and also lscpu claims CPU(s): 1).
The very same kernel, when run on an Intel i5-7440EQ, returns nproc=4,
which is correct.
I'm using CONFIG_GENERIC_CPU=y, and this, to my knowledge, should be a
safer option to handle both Atom and i5 or other platforms. I've also
tried to use CONFIG_MATOM or CONFIG_MCORE2 without noticeable
differences.

I attach here the full config and the dmesg that I obtain on the two
platforms. Comparing the logs I've noticed the message "BIOS bug, no
explicit IRQ entries, using default mptable. (tell your hw vendor)"
but I'm not sure whether this is the cause or an effect of the
problem.

Can you help me suggesting which CONFIG option I should change?

Regards,

    Davide
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Re: Wrong CPU count on Apollo Lake platform

[Jan Kiszka]

On 20.05.22 13:41, dabbede--- via Xenomai wrote:
> Dear Xenomai community,
> 
> I'm writing here because of the following issue: I have compiled a
> xenomai-patched kernel that, when used on an Intel Atom E3950 (Apollo
> Lake family), return the wrong cpu count (i.e. nproc returns 1 instead
> of 4, and also lscpu claims CPU(s): 1).
> The very same kernel, when run on an Intel i5-7440EQ, returns nproc=4,
> which is correct.
> I'm using CONFIG_GENERIC_CPU=y, and this, to my knowledge, should be a
> safer option to handle both Atom and i5 or other platforms. I've also
> tried to use CONFIG_MATOM or CONFIG_MCORE2 without noticeable
> differences.
> 
> I attach here the full config and the dmesg that I obtain on the two
> platforms. Comparing the logs I've noticed the message "BIOS bug, no
> explicit IRQ entries, using default mptable. (tell your hw vendor)"
> but I'm not sure whether this is the cause or an effect of the
> problem.
> 
> Can you help me suggesting which CONFIG option I should change?
> 

[    0.057400] Processor #0 (Bootup-CPU)
[    0.057403] BIOS bug, no explicit IRQ entries, using default mptable. (tell your hw vendor)
[    0.057412] Processors: 1
[    0.057416] smpboot: Allowing 1 CPUs, 0 hotplug CPUs

Seems first of all unrelated to Xenomai.

Did you already try to compile a Xenomai/I-pipe free kernel with 
defconfig settings, whether that is able to detect all CPUs? If not, you 
should really look for a BIOS update of your board. Or complain with its 
vendor about breaking standards and, thus, Linux.

Jan

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Siemens AG, Technology
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