Re: parallel is slower than serial
Thank you, folks, for your hints and suggestions! Indeed, I re-wrote the code and got it substantially faster and well paralleled. Insted of making inner loop parallel, I made parallel both of them. For that I had to convert 2d index into 1d, and then back to 2d. Essentially I had to calculate each element Aij of the matrix, and then I put everything to 1d array. And yes, A = A ~ Aij was very slow, to avoid it I had to use 2d -> 1d mapping. I will check your solution as well as I like it too. The more I use the D Language, the more I like it. On Tuesday, 18 October 2022 at 16:07:22 UTC, Siarhei Siamashka wrote: On Tuesday, 18 October 2022 at 11:56:30 UTC, Yura wrote: ```D // Then for each Sphere, i.e. dot[i] // I need to do some arithmetics with itself and other dots // I have only parallelized the inner loop, i is fixed. It's usually a much better idea to parallelize the outer loop. Even OpenMP tutorials explain this: https://ppc.cs.aalto.fi/ch3/nested/ (check the "collapse it into one loop" suggestion from it). ```D for (auto j=0;j This way of appending to an array is very slow and `A ~= Ai[j];` is much faster. And even better would be `A ~= Ai;` instead of the whole loop.
Re: parallel is slower than serial
On 10/18/22 06:24, Guillaume Piolat wrote: > To win something with OS threads, you must think of tasks that takes on > the order of milliseconds rather than less than 0.1ms. > Else you will just pay extra in synchronization costs. In other words, the OP can adjust work unit size. It is on the official documentation but I also mention it on slide 72 of the section that starts at the following point: https://youtu.be/dRORNQIB2wA?t=1327 Ali
Re: parallel is slower than serial
On Tuesday, 18 October 2022 at 11:56:30 UTC, Yura wrote: ```D // Then for each Sphere, i.e. dot[i] // I need to do some arithmetics with itself and other dots // I have only parallelized the inner loop, i is fixed. It's usually a much better idea to parallelize the outer loop. Even OpenMP tutorials explain this: https://ppc.cs.aalto.fi/ch3/nested/ (check the "collapse it into one loop" suggestion from it). ```D for (auto j=0;j This way of appending to an array is very slow and `A ~= Ai[j];` is much faster. And even better would be `A ~= Ai;` instead of the whole loop.
Re: parallel is slower than serial
On Tuesday, 18 October 2022 at 11:56:30 UTC, Yura wrote: What I am doing wrong? The size of your task are way too small. To win something with OS threads, you must think of tasks that takes on the order of milliseconds rather than less than 0.1ms. Else you will just pay extra in synchronization costs.
parallel is slower than serial
Dear All,
I am trying to make a simple code run in parallel. The parallel
version works, and gives the same number as serial albeit slower.
First, the parallel features I am using:
import core.thread: Thread;
import std.range;
import std.parallelism:parallel;
import std.parallelism:taskPool;
import std.parallelism:totalCPUs;
// Then, I have an array of structures
shared Sphere [] dot;
// Each Sphere is
struct Sphere {
string El;
double x;
double y;
double z;
double S;
double Z;
double V;
}
// Then for each Sphere, i.e. dot[i]
// I need to do some arithmetics with itself and other dots
// I have only parallelized the inner loop, i is fixed.
// parallel loop
auto I = std.range.iota(0,dot.length);
shared double [] Ai;
Ai.length = dot.length;
foreach (j;parallel(I)) {
Ai[j] = GETAij (i, j, dot[i], dot[j]);
}
for (auto j=0;jWhat I am doing wrong? Any advanced options for the ldc2
compiler? Many thanks in advance!
