[Pw_forum] System memory issue using --with-pinned-mem on QE-GPU

[Filippo SPIGA]

On Jan 21, 2016, at 12:35 AM, Rolly Ng <rollyng at gmail.com> wrote:
> My server has total of 144GB RAM and 8x C2050. These cards have 3GB memory each, so there are 24 GB of video RAM. If I compile px-gpu.x with the option "--with-pinned-mem", does it lock 24GB of system memory out of 144 GB? and I will have 120 GB system RAM left?

Not exaclty, it "locks" a portion of the CPU memory but it depends by the input and not by the amount of memory on the GPU. It should be less but it depends by the input case (since specific data structures are "pinned", others are not). By default, very little data structures that are transferred to the GPU are already allocated as page-locked. 

Give it a try, if you calculation starts a complete few SCF iterations then more likely will run until the very end. You may experience a bit (but a very little) increase in performance. But if too much memory is pinned, the system can get slow. It is not intuitive why but it can happen.

HTH

--
Mr. Filippo SPIGA, M.Sc.
Quantum ESPRESSO Foundation
http://www.quantum-espresso.org ~ skype: filippo.spiga

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