[Pw_forum] why pw.x runs at similar speed using 8 cores or 16 cores
igirotto at ictp.it
Mon Sep 21 16:35:09 CEST 2015
scaling depends in general by number of factors. Moreover, you are
providing no information about your input system.
This results in a too generic question which is hard to answer if not
making other questions (to be generally avoided on mailing lists).
I reckon you registered a better scaling from 2 to 4 cores and from 4 to
8 cores as you are reporting the issue only about scaling from 8 to 16
By experience I would say that you are dumping into two possible scenarios:
1) You reached a scaling limits.
In general px.x scales well up to 16 processes except you are working
with a really small system.
2) You are actually working on a two quad-core CPU system with
The hyper-threading extends to 8 the number of virtual cores per CPU
socket (your /proc/cpuinfo reports 16 cores).
In most cases, high-performance software applications (such as QE) do
not benefit of this feature scaling only up to the number of physical
Possibly you can google the model of you processor (see /proc/cpuinfo)
to verify the number of physical cores on each CPU socket.
On 15/09/2015 03:40, Shaofeng Wang wrote:
> Dear all,
> I got a server computer equipped with two 8 core cpus. I installed
> intel fortran compiler (12.1) and openmpi (1.6.5). No errors took
> place during installation. Then I compiled parallel quantum esspresso
> (5.2.0) and the program run correctly. However, I found pw.x runs at
> very similar speed with 8 cores or 16 cores. Could any expert show me
> how to improve the calculation speed?
> The make.sys file is attached.
> Thanks in advance.
> Shaofeng Wang, Ph.D of Geochemistry
> Environmental Molecular Science Group
> Institute of Applied Ecology, Chinese Academy of Sciences
> Shenyang, 110016, China
> wangshaofeng at iae.ac.cn
> Pw_forum mailing list
> Pw_forum at pwscf.org
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