Search found 808 matches

by MarkB
Thu Mar 11, 2021 11:03 am
Forum: Using OpenMP
Topic: How to run OpenMP code on MPI (HPC) - virtualisation ?
Replies: 1
Views: 18105

Re: How to run OpenMP code on MPI (HPC) - virtualisation ?

You should be able to run your OpenMP code on a single node of the HPC system - depending on how new the system is there could be anything from about 16 to over 100 cores per node. There is usually no way to run OpenMP codes across more than one node or on top of MPI. It is technically possible, but...
by MarkB
Tue Jan 26, 2021 1:52 am
Forum: Using OpenMP
Topic: Conditional change in shared variable
Replies: 1
Views: 11425

Re: Conditional change in shared variable

If you were just counting non-zeros, a reduction would work fine. The problem is with using nnz as an index into i2. If you don't mind the order of the values in i2 being non-deterministic, you can do this with an extra private variable and atomic capture: nnz=0 !$omp parallel do default(private) sc...
by MarkB
Tue Jan 26, 2021 1:31 am
Forum: Using OpenMP
Topic: While loop in Julia's collection
Replies: 1
Views: 11524

Re: While loop in Julia's collection

You can't parallelise the while loop - there is a dependency between iterations on the value of z. I don't think you can do much better than this, except perhaps to experiment with other loop scheduling options/chunksizes.
by MarkB
Mon Dec 21, 2020 2:07 am
Forum: Using OpenMP
Topic: macOS Big Sur
Replies: 2
Views: 13051

Re: macOS Big Sur

OpenMP has no control over vendor's releases, so I'm afraid this is entirely down to Apple!

As far as I know the situation for Big Sur has not changed from other recent MacOS versions - you need a separate compiler install to support OpenMP.
by MarkB
Mon Nov 30, 2020 1:01 pm
Forum: Using OpenMP
Topic: Collapse not working
Replies: 3
Views: 12858

Re: Collapse not working

I presume that the 1-thread performance of the collapsed version is also bad? It's quite rare, but I do see this kind of thing once in a while - the OpenMP directives cause the compiler optimisation to fail in some way. In this case it might be the address computations that are the problem. Sometime...
by MarkB
Tue Aug 11, 2020 8:31 am
Forum: Using OpenMP
Topic: Tasks executed by thread 0 only
Replies: 2
Views: 14243

Re: Tasks executed by thread 0 only

There is no way to specify which thread executes a task. Most likely you do not need to restrict file I/O to thread 0, as long as you don't have multiple tasks/threads trying to write the same file concurrently. But a pattern like this might work for you: #pragma omp parallel { #pragma omp master { ...
by MarkB
Fri Jul 24, 2020 1:51 pm
Forum: Using OpenMP
Topic: loop
Replies: 1
Views: 12736

Re: loop

Where is normal_fact modified? (Your code snippet doesn't show this).
by MarkB
Thu Jun 18, 2020 2:41 am
Forum: Using OpenMP
Topic: OPENMP Performance Problem
Replies: 3
Views: 13366

Re: OPENMP Performance Problem

The OpenMP runtime will create threads even though the parallel region does nothing, and these may well stay alive and consume CPU resources outside of the parallel regions. What could be happening is that the threads are being bound to the same core as the MPI process. You may need to set some flag...
by MarkB
Tue Jun 16, 2020 5:53 am
Forum: Using OpenMP
Topic: parallel http requests program
Replies: 1
Views: 12144

Re: parallel http requests program

This is a rather unusual use case for OpenMP - normally it is used for compute intensive tasks. I think the performance of this code will be be very dependent on your I/O and network bandwidth.
by MarkB
Tue Jun 16, 2020 5:46 am
Forum: Using OpenMP
Topic: OPENMP Performance Problem
Replies: 3
Views: 13366

Re: OPENMP Performance Problem

What are you using to measure the execution time?