[Pw_forum] Computational Speed for pw.x

[Lorenzo Paulatto]

On 07/12/17 12:40, Sitangshu Bhattacharya wrote:
> As per my experience, QE/VASP or any other such computations which uses 
> openmpi supports 2^n core processors. 

Just to be clear: QE can use any number of CPUs, being a power of 2 or 
not does not matter.

kind regards

This is actually total number of
> core per physical processor multiplied by 2 (hyperthreaded), check by 
> typing "htop" in your terminal. You may try locating the wall time 
> results done at different no. of cores for your computations. The 
> results might be a bit faster if you use 32 instead of 40 (and so on) 
> and divide them into pools. Please note that inter-node communications 
> in PWSCF is the main bottleneck and depends on the 100GBpS or more 
> connectivity switch. Eagerly waiting for this to be taken care by QE 
> experts!. Image parallelization is supported by the Ph.x code, however 
> collecting the results is a bit tricky if you are doing 2nd or 3rd order 
> corrections. Parallelizing diagonalization technique make my computation 
> a bit slower, probably due to the the less no. of atoms involved or so.
> Check with -np 2 only, first on a simple structure like Si and then 
> increase this no. to see if this is taking more/less time. You will get 
> an idea atleast..
> 
> Regards
> 
> On Thu, Dec 7, 2017 at 2:50 PM, Amar Singh 
> <amarsingh122014 at rediffmail.com <mailto:amarsingh122014 at rediffmail.com>> 
> wrote:
> 
>     Dear Dr. Bhattacharya,
>     ​Thanks for the link. Though, being very naïve to such computation,
>     I am not able to figure out the best possible set of parameters I
>     should start with. Would be thankful if you can suggest some typical
>     values for -np, -ni, -nk, -nt and -nd for the system with 40
>     processors and 256 GB RAM.
>     ​thanks
>     Amar
> 
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> 
> -- 
> **********************************************
> Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D
> Assistant Professor,
> Room No. 2221, CC-1,
> Nanoscale Electro-Thermal Laboratory,
> Department of Electrical and Communication Engineering,
> Indian Institute of Information Technology-Allahabad
> Uttar Pradesh 211 012
> India
> Telephone: 91-532-2922000 Extn.: 2131
> Web-page: http://profile.iiita.ac.in/sitangshu/
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-- 
Lorenzo Paulatto - Paris