[QE-users] QE+LIBXC on AMD EPYC CPUs poor performances

[Giuseppe Zollo]

Dear Pietro,
thank you so much. It was surprising to me too, but this is what I've got.
Surfing on the internet, I've received some indications of similar problems
with AMD architectures. In my case this problem emerges ONLY when libxc is
involved, even using a very basic MPI approach (no OpenMP... that makes the
situation even worse, especially for INTEL+MKL compilations).
Without libxc, everything works perfectly.
Although it seems that you have not received similar reports so far, it is
a bit embarrassing that 128 MPI AMD EPYC 7713 performs worse than 32
MPI Xeon(R)
Gold 6226R when using r2SCAN that involves dense grids and massive memory
handling tasks.
Btw, thank you for your suggestion concerning QE7.6: I'll check it as soon
as the new version is released.
I'll keep you informed
Giuseppe


Il giorno ven 24 lug 2026 alle ore 09:34 Pietro Davide Delugas <
pdelugas at sissa.it> ha scritto:

> Dear Giuseppe, this is very strange.  There is nothing tightly
> CPU-architecture-specific in those code parts; it's plain Fortran.
> Architecture-specific optimisation is expected from the Fortran compiler;
> in my experience, gfortran is equally not the best for both architectures
> (and whether good or bad, it would be equally good or bad for all the code,
> not just for one single kernel).  Intel and AOCC compilers usually do much
> better architecture-specific optimisation.
>
>
> The first thing to check is that you are actually using only the physical
> cores, so (number of MPI ranks) × (number of OpenMP threads per process)
> should be at most 128, assuming nothing else heavy is running on the
> machine. Use the env variable OMP_NUM_THREADS to set the number of OpenMP
> threads per process.
>
> That said, on general grounds, 7.6 will be available on the Quantum
> Espresso website by this weekend, and pw behaviour with SCAN and R2SCAN
> will be significantly improved.  Better give it a try next week.
> Pietro
> ------------------------------
> *From:* users <users-bounces at lists.quantum-espresso.org> on behalf of
> Giuseppe Zollo via users <users at lists.quantum-espresso.org>
> *Sent:* Thursday, July 23, 2026 16:31
> *To:* users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
> *Subject:* [QE-users] QE+LIBXC on AMD EPYC CPUs poor performances
>
> Dear all,
> I'm experiencing very very poor behavior of QE 7.5 + LIBXC 7.0.0 on AMD
> EPYC 7713 CPU regardless of the compilation. I've compiled using gcc+
> native AMD libraries aocl or gcc+MKL or intel+MKL. In any case, after
> successful compilation, I receive very poor behavior using r2SCAN meta-GGA.
> The system is not large  (less than 130 atoms) and the same calculation
> behaves reasonably well on two Intel(R) Xeon(R) Gold 6226R (16 cores
> each) (much older and much lower benchmark), nearly 300 secs per scf
> iteration step. Using two AMD EPYC 7713 cpus (64 cores each, much faster
> and with NUMA access) the performance is even worse than two Xeon(R) Gold
> 6226R.
> I've spent days trying to fix it and it seems it could be related to the
> AMD EPYC architecture.
> I wonder if anyone has experienced the same and if there are indications
> on how to handle this drawback.
> Thanks
> Giuseppe
>
> --
> Giuseppe Zollo
> Dipartimento di Scienze di base e Applicate per l'Ingegneria
> University "La Sapienza" of Rome
> via A. Scarpa 14-16, Rome-Italy
> phone: +39 06 49766947
>
> *Fai crescere le giovani ricercatrici e i giovani ricercatori*
>
> *con il 5 per mille alla Sapienza*
>
> Scrivi il codice fiscale dell'Università
> *80209930587 **Cinque per mille* <https://www.uniroma1.it/it/node/23149>
>


-- 
Giuseppe Zollo
Dipartimento di Scienze di base e Applicate per l'Ingegneria
University "La Sapienza" of Rome
via A. Scarpa 14-16, Rome-Italy
phone: +39 06 49766947

-- 


*Fai crescere le giovani ricercatrici e i giovani ricercatori***

*con il 
5 per mille alla Sapienza*

Scrivi il codice fiscale dell'Università 
*80209930587
**Cinque per mille <https://www.uniroma1.it/it/node/23149>*
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