Text buffering on HPE Cray system

[asrosen]

Hello,

After successfully compiling VASP on an HPE Cray system (https://docs.ncsa.illinois.edu/systems/ ... /en/latest), I found that the text in the OUTCAR is not generated in real-time. For instance, it will update every ~5 SCF iterations. Similarly, the OSZICAR is not populated until the end of the run. I have seen this behavior on other machines before, but I'm curious if there is a way to modify this behavior so that everything is generated in real-time without any buffering.

[michael_wolloch]

Hi Andrew,

This is indeed an issue we have faced on Cray machines, which are only writing output if buffers are explicitly flushed (which VASP does not do) or overflowing. The behaviour of srun can be changed by the --unbuffered option. Try:

Code: Select all

srun --unbuffered /path/to/your/vasp/bin/vasp_std

However, I would not recommend enabling this runtime option for production, since it could degrade performance. For debugging and developing it has served us well, however. Note that we did not try this on your machine specifically, and not with NVIDIA's compilers.

Cheers, Michael