[cfarm-users] Fixing CPU/core/threads count

[Zach van Rijn]

On Sun, 2020-07-05 at 23:24 +0200, Baptiste Jonglez via cfarm-users
wrote:
> Hi Brice,
> 
> On 04-04-20, Brice Goglin wrote:
> > Le 04/04/2020 à 20:28, Baptiste Jonglez a écrit :
> > > Following up on a thread from 2018 [1], we still have issue with
> > > counting
> > > the number of CPU, cores and threads on "exotic" machines.
> 
> We encountered another interesting case: on the new gcc102 machine
> with a Sparc T3 CPU, hwloc reports 64 cores, while there are actually
> only 32 cores (2 sockets x 16 cores).
> 
> hwloc apparently thinks that there are 4 threads per core, instead of
> the correct value 8.

On Sun, 2020-07-05 at 23:11 +0200, Baptiste Jonglez wrote:
> ...
> I am fixing the core count and will ask hwloc's author about
> this.

One funny thing I've observed previously:

for k in $(seq 0 $(($(nproc)-1))); do
    cat /sys/devices/system/cpu/cpu$k/topology/thread_siblings;
done

prints:

...,00000000,00000000,00000000,0000000f
...,00000000,00000000,00000000,0000000f
...,00000000,00000000,00000000,0000000f
...,00000000,00000000,00000000,0000000f
...,00000000,00000000,00000000,000000f0
...,00000000,00000000,00000000,000000f0
...,00000000,00000000,00000000,000000f0
...,00000000,00000000,00000000,000000f0
...

(or friendlier thread_siblings_list):

0-3
0-3
0-3
0-3
4-7
4-7
4-7
4-7
8-11
8-11
...

instead of what I would expect:

0-7
0-7
0-7
0-7
0-7
0-7
0-7
0-7
8-15
8-15
8-15
8-15
8-15
8-15
8-15
8-15
...


perhaps this is related?


ZV